Golf balls having a center with surrounding foam outer core layer

ABSTRACT

Multi-layered golf balls having a dual-layered core and cover of at least one layer are provided. The dual-core construction includes a non-foamed inner core (center) made of a thermoplastic or thermoset composition such as polybutadiene rubber. An outer core layer comprising a foamed composition, such as polyurethane foam, is disposed about the inner core. In one version, the foamed outer core layer is made of a relatively soft foam composition having low flex modulus and density. The foamed outer core layer may specific gravity gradient within the layer, wherein the outer surface specific gravity is greater than the midpoint specific gravity. A cover may be disposed about the core structure. For example, an inner cover made of ethylene acid copolymer ionomer and outer cover made of polyurethane may be used.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending, co-assigned,U.S. patent application Ser. No. 14/243,156 filed on Apr. 2, 2014, nowabandoned the entire disclosure of which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to multi-piece, golf ballshaving a solid core made of non-foamed and foamed compositions.Particularly, the dual-layered core has a non-foamed inner core (center)and surrounding foamed outer core layer. A thermoset or thermoplasticpolymer material may be used to form the center and polybutadiene rubberis preferably used. Preferably, a relatively soft polyurethane foamcomposition is used to form the outer core layer. The core layers mayhave different flex modulus, hardness, and specific gravity values. Theball further includes a cover of at least one layer.

Brief Review of the Related Art

Both professional and amateur golfer use multi-piece, solid golf ballstoday. Basically, a two-piece solid golf ball includes a solid innercore protected by an outer cover. Normally, the inner core is made of anatural or synthetic rubber such as polybutadiene, styrene butadiene, orpolyisoprene. The cover surrounds the inner core and may be made of avariety of materials including ethylene acid copolymer ionomers,polyamides, polyesters, polyurethanes, and polyureas.

In recent years, three-piece, four-piece, and even five-piece balls havebecome more popular. New manufacturing technologies, lower materialcosts, and desirable ball playing performance properties havecontributed to these multi-piece balls becoming more popular. Many golfballs used today have multi-layered cores comprising an inner core andat least one surrounding outer core layer. For example, the inner coremay be made of a relatively soft and resilient material, while the outercore may be made of a harder and more rigid material. The “dual-core”subassembly is encapsulated by a cover of at least one layer to make afinished ball. Different materials can be used to manufacture the coreand cover layers and provide various properties to the finished ball.

In general, dual-cores comprising an inner core (or center) and asurrounding outer core layer are known in the industry. For example,Chikaraishi et al., U.S. Pat. No. 5,048,838 discloses a three-piece golfball containing a two-piece solid core and a cover. The dense inner corehas a diameter in the range of 15-25 mm with a specific gravity of 1.2to 4.0 and the outer core layer has a specific gravity of 0.1 to 3.0less than the specific gravity of the inner core. The inner and outercores are made of rubber compositions. Watanabe, U.S. Pat. No. 7,160,208discloses a three-piece golf ball comprising a rubber-based inner core;a rubber-based outer core layer; and a polyurethane elastomer-basedcover. The inner core layer has a JIS-C hardness of 50 to 85; the outercore layer has a JIS-C hardness of 70 to 90; and the cover has a Shore Dhardness of 46 to 55. Also, the inner core has a specific gravity ofmore than 1.0, and the core outer layer has a specific gravity equal toor greater than that of that of the inner core.

The core sub-structure located inside of the golf ball acts as an engineor spring for the ball. Thus, the composition and construction of thecore is a key factor in determining the resiliency and reboundingperformance of the ball. In general, the rebounding performance of theball is determined by calculating its initial velocity after beingstruck by the face of the golf club and its outgoing velocity aftermaking impact with a hard surface. More particularly, the “Coefficientof Restitution” or “COR” of a golf ball refers to the ratio of a ball'srebound velocity to its initial incoming velocity when the ball is firedout of an air cannon into a rigid vertical plate. The COR for a golfball is written as a decimal value between zero and one. A golf ball mayhave different COR values at different initial velocities. The UnitedStates Golf Association (USGA) sets limits on the initial velocity ofthe ball so one objective of golf ball manufacturers is to maximize CORunder such conditions. Balls with a higher rebound velocity have ahigher COR value. Such golf balls rebound faster, retain more totalenergy when struck with a club, and have longer flight distance asopposed to balls with low COR values. These properties are particularlyimportant for long distance shots. For example, balls having highresiliency and COR values tend to travel a far distance when struck by adriver club from a tee.

The durability, spin rate, and feel of the ball also are importantproperties. In general, the durability of the ball refers to theimpact-resistance of the ball. Balls having low durability appear wornand damaged even when such balls are used only for brief time periods.In some instances, the cover may be cracked or torn. The spin raterefers to the ball's rate of rotation after it is hit by a club. Ballshaving a relatively high spin rate are advantageous for short distanceshots made with irons and wedges. Professional and highly skilledamateur golfers can place a back spin more easily on such balls. Thishelps a player better control the ball and improves shot accuracy andplacement. By placing the right amount of spin on the ball, the playercan get the ball to stop precisely on the green or place a fade on theball during approach shots. On the other hand, recreational players whocannot intentionally control the spin of the ball when hitting it with aclub are less likely to use high spin balls. For such players, the ballcan spin sideways more easily and drift far-off the course, especiallyif it is hooked or sliced. Meanwhile, the “feel” of the ball generallyrefers to the sensation that a player experiences when striking the ballwith the club and it is a difficult property to quantify. Most playersprefer balls having a soft feel, because the player experience a morenatural and comfortable sensation when their club face makes contactwith these balls. Balls having a softer feel are particularly desirablewhen making short shots around the green, because the player senses morewith such balls. The feel of the ball primarily depends upon thehardness and compression of the ball.

Manufacturers of golf balls are constantly looking to differentmaterials and ball constructions for improving the playing performanceand other properties of the ball. For example, hard and durablematerials having a relatively high flex modulus can be used to make arelatively hard core. The resulting golf ball tends to travel a longdistance because of the high velocity imparted by the hard core.However, one disadvantage with these harder balls is they tend toprovide the golfer with a rougher and harder “feel.” Thus, the playermay experience a more uncomfortable and unnatural sensation as the clubface makes impact with the ball. Moreover, the player tends to have lesscontrol when hitting relatively hard balls. It generally is moredifficult to hit hard balls with the proper touch and spin.

To address these problems, golf ball manufacturers have looked at softerand lighter-weight materials, such as foams, for making the inner core.For example, Puckett and Cadorniga, U.S. Pat. Nos. 4,836,552 and4,839,116 disclose one-piece, short distance golf balls made of a foamcomposition comprising a thermoplastic polymer (ethylene acid copolymerionomer such as Surlyn®) and filler material (microscopic glassbubbles). The density of the composition increases from the center tothe surface of the ball. Thus, the ball has relatively dense outer skinand a cellular inner core. According to the '552 and '116 patents, byproviding a short distance golf ball, which will play approximately 50%of the distance of a conventional golf ball, the land requirements for agolf course can be reduced 67% to 50%.

Gentiluomo, U.S. Pat. No. 5,104,126 discloses a three-piece ball with adense inner core made of steel, lead, brass, zinc, copper, and a filledelastomer, wherein the core has a specific gravity of at least 1.25. Theinner core is encapsulated by a lower density syntactic foamcomposition, and the core construction is encapsulated by an ionomercover. Yabuki et al., U.S. Pat. No. 5,482,285 discloses a three-piecegolf ball having an inner core and outer core encapsulated by an ionomercover. The specific gravity of the outer core is reduced so that itfalls within the range of 0.2 to 1.0. The specific gravity of the innercore is adjusted accordingly so that the total weight of the inner/outercore falls within a range of 32.0 to 39.0 g. The inner core may beformed of a rubber composition and the outer core may be formed of afoamed resin such as an ionomer polyethylene, or polystyrene resin, or athermosetting resin such as a phenol resin.

Aoyama, U.S. Pat. Nos. 5,688,192 and 5,823,889 disclose a golf ballcontaining a core, wherein the core comprises an inner and outerportion, and a cover made of a material such as balata rubber orethylene acid copolymer ionomer. The core is made by foaming, injectinga compressible material, gasses, blowing agents, or gas-containingmicrospheres into polybutadiene or other core material. According to the'889 patent, polyurethane compositions may be used. The compressiblematerial, for example, gas-containing compressible cells may bedispersed in a limited part of the core so that the portion containingthe compressible material has a specific gravity of greater than 1.00.

Sullivan and Binette, U.S. Pat. No. 5,833,553 discloses a golf ballhaving core with a coefficient of restitution of at least 0.650 and acover with a thickness of at least 3.6 mm (0.142 inches) and a Shore Dhardness of at least 60. According to the '553 patent, the combinationof a soft core with a thick, hard cover results in a ball having betterdistance. The '553 patent discloses that the core may be formed from auniform composition or may be a dual or multi-layer core, and it may befoamed or unfoamed. Polybutadiene rubber, natural rubber, metallocenecatalyzed polyolefins, and polyurethanes are described as being suitablematerials for making the core.

Sullivan and Ladd, U.S. Pat. No. 6,688,991 discloses a golf ballcontaining a low specific gravity core and an optional intermediatelayer. This subassembly is encased within a high specific gravity coverwith Shore D hardness in the range of about 40 to about 80. The core ispreferably made from a highly neutralized thermoplastic polymer such asethylene acid copolymer which has been foamed. The cover preferably hashigh specific gravity fillers dispersed therein.

Nesbitt, U.S. Pat. No. 6,767,294 discloses a golf ball comprising: i) apressurized foamed inner center formed from a thermoset material, athermoplastic material, or combinations thereof, a blowing agent and across-linking agent and, ii) an outer core layer formed from a secondthermoset material, a thermoplastic material, or combinations thereof.Additionally, a barrier resin or film can be applied over the outer corelayer to reduce the diffusion of the internal gas and pressure from thenucleus (center and outer core layer). Preferred polymers for thebarrier layer have low permeability such as Saran® film (poly(vinylidene chloride), Barex® resin (acyrlonitrile-co-methyl acrylate),poly (vinyl alcohol), and PET film (polyethylene terephthalate). The'294 patent does not disclose core layers having different hardnessgradients.

Sullivan, Ladd, and Hebert, U.S. Pat. No. 7,708,654 discloses a golfball having a foamed intermediate layer. Referring to FIG. 1 in the '654patent, the golf ball includes a core (12), an intermediate layer (14)made of a highly neutralized polymer having a reduced specific gravity(less than 0.95), and a cover (16). According to the '654 patent, theintermediate layer can be an outer core, a mantle layer, or an innercover. The reduction in specific gravity of the intermediate layer iscaused by foaming the composition of the layer and this reduction can beas high as 30%. The '654 patent discloses that other foamed compositionssuch as foamed polyurethanes and polyureas may be used to form theintermediate layer.

Tutmark, U.S. Pat. No. 8,272,971 is directed to golf balls containing anelement that reduces the distance of the ball's flight path. In oneembodiment, the ball includes a core and cover. A cavity is formedbetween core and cover and this may be filled by a foamed polyurethane“middle layer” in order to dampen the ball's flight properties. The foamof the middle layer is relatively light in weight; and the core isrelatively heavy and dense. According to the '971 patent, when a golferstrikes the ball with a club, the foam in the middle layer actuates andcompresses, thereby absorbing much of the impact from the impact of theball.

However, one disadvantage with golf balls having a foam core is the balltends to have low resiliency. That is, the velocity of the ball tends tobe low after being hit by a club and the ball generally travels shortdistances. It would be desirable to have a foam core that provides theball with good resiliency as well as a nice feel. Such balls would allowplayers to generate higher initial ball speed when striking the ballwhile also retaining a soft feel and comfort level. Particularly, itwould be desirable to develop multi-layered foam core constructionshaving high resiliency and soft compression so the ball had both longdistance and spin control properties. These ball properties would helpthe golfer make better shots with drives off the tee and approach shotsnear the green. The present invention provides new foam coreconstructions having such properties as well as other advantageousfeatures and benefits. The invention also encompasses golf ballscontaining the improved core constructions.

SUMMARY OF THE INVENTION

The present invention provides a multi-layered golf ball comprising acore comprising an inner core layer (center); outer core layer; andcover having at least one layer. In one version, the ball includes acore subassembly comprising: i) an inner core layer comprising anon-foamed thermoset or thermoplastic composition, wherein the innercore has a diameter in the range of about 0.750 to about 1.500 inches,and ii) an outer core layer comprising a foamed composition, wherein theouter core layer is disposed about the inner core and has a thickness inthe range of about 0.025 to about 0.800 inches. The inner core has aspecific gravity (SG_(inner)) and a flex modulus (FM_(inner)), and theouter core has a specific gravity (SG_(outer)) and a flex modulus(FM_(outer)), and preferably the SG_(inner) is greater than theSG_(outer), and the FM_(inner) is greater than the FM_(outer).

In one preferred version, the FM_(inner) is in the range of about 5,000to about 60,000 psi; and the FM_(outer) is in the range of about 100 toabout 10,000 psi. Preferably, the FM_(inner) is at least 20% greaterthan the FM_(outer). In one embodiment, the inner core has a diameter inthe range of about 0.90 to about 1.40 inches and specific gravity in therange of about 0.60 to about 2.90 g/cc. Meanwhile, in one embodiment,the outer core layer has a thickness in the range of about 0.050 toabout 0.300 inches and specific gravity in the range of about 0.20 toabout 0.95 g/cc.

Non-foamed thermoset or thermoplastic materials are used to form theinner core layer. For example, polybutadiene rubber may be used. Inanother example, an ionomer composition comprising an O/X/Y-typecopolymer, wherein O is α-olefin, X is a C₃-C₈ α,β-ethylenicallyunsaturated carboxylic acid present in an amount of 5 to 20 wt. %, and Yis an acrylate selected from alkyl acrylates and aryl acrylates, whereingreater than 70% of the acid groups are neutralized with a metal ion isused. In one version, the outer core comprises a foam polyurethanecomposition prepared from a mixture comprising polyisocyanate, polyol,and curing agent compounds, and blowing agent. Aromatic and aliphaticpolyisocyanates may be used. The foamed polyurethane composition may beprepared by using water as a blowing agent. The water is added to themixture in a sufficient amount to cause the mixture to foam.Surfactants, catalysts, mineral fillers, and other additives may beincluded in the mixture.

The core layers may have different hardness gradients. For example, eachcore layer may have a positive, zero, or negative hardness gradient. Ina first embodiment, the inner core has a positive hardness gradient; andthe outer core layer has a positive hardness gradient. In a secondembodiment, the inner core has a positive hardness gradient, and theouter core layer has zero or negative hardness gradient. In yet anotherversion, the inner core has a zero or negative hardness gradient; andthe outer core layer has a positive hardness gradient. In anotheralternative version, both the inner and outer core layers have zero ornegative hardness gradients.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are characteristic of the present invention areset forth in the appended claims. However, the preferred embodiments ofthe invention, together with further objects and attendant advantages,are best understood by reference to the following detailed descriptionin connection with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a dual-layered core subassembly madein accordance with the present invention;

FIG. 2 is a cross-sectional view of a three-piece golf ball having adual-layered core made in accordance with the present invention;

FIG. 3 is a cross-sectional view of a four-piece golf ball having adual-layered core made in accordance with the present invention;

FIG. 4 is a perspective view of a finished golf ball made in accordancewith the present invention;

FIG. 5 is a is a cross-sectional view of a dual-core assembly includingan inner core and surrounding outer core layer showing a foamedgeometric midpoint, outer region, and outer surface skin in the outercore, the core assembly being made in accordance with the presentinvention; and

FIG. 6 is a is a cross-sectional view of a dual-core assembly includingan inner core and surrounding outer core layer showing a foamedgeometric midpoint, partially-collapsed foamed outer region, and outersurface skin; and a surrounding inner cover layer, the core assembly andinner cover being made in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Golf Ball Constructions

Golf balls having various constructions may be made in accordance withthis invention. For example, golf balls having three piece, four-piece,and five-piece constructions with single or multi-layered covermaterials may be made. Representative illustrations of such golf ballconstructions are provided and discussed further below. The term,“layer” as used herein means generally any spherical portion of the golfball. More particularly, in one version, a three-piece golf ballcontaining a dual-layered core and single-layered cover is made. Thedual-core includes an inner core (center) and surrounding outer corelayer. In another version, a four-piece golf ball containing a dual-coreand dual-cover (inner cover and outer cover layers) is made. In yetanother construction, a four-piece or five-piece golf ball containing adual-core; casing layer(s); and cover layer(s) may be made. As usedherein, the term, “casing layer” means a layer of the ball disposedbetween the multi-layered core subassembly and cover. The casing layeralso may be referred to as a mantle or intermediate layer. The diameterand thickness of the different layers along with properties such ashardness and compression may vary depending upon the construction anddesired playing performance properties of the golf ball.

Inner Core Composition

As discussed above, a two-layered or dual-core is preferably made,wherein the inner core (center) is surrounded by an outer core layer,and the center is made from a non-foamed composition. In one preferredembodiment, the inner core layer is made from a non-foamed thermosetcomposition and more preferably from a non-foamed thermoset rubbercomposition.

Suitable thermoset rubber materials that may be used to form the innercore layer (center) include, but are not limited to, polybutadiene,polyisoprene, ethylene propylene rubber (“EPR”),ethylene-propylene-diene (“EPDM”) rubber, styrene-butadiene rubber,styrenic block copolymer rubbers (such as “SI”, “SIS”, “SB”, “SBS”,“SIBS”, and the like, where “S” is styrene, “I” is isobutylene, and “B”is butadiene), polyalkenamers such as, for example, polyoctenamer, butylrubber, halobutyl rubber, polystyrene elastomers, polyethyleneelastomers, polyurethane elastomers, polyurea elastomers,metallocene-catalyzed elastomers and plastomers, copolymers ofisobutylene and p-alkylstyrene, halogenated copolymers of isobutyleneand p-alkylstyrene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and blends of two or morethereof. Preferably, the outer core layer is formed from a polybutadienerubber composition.

The thermoset rubber composition may be cured using conventional curingprocesses. Suitable curing processes include, for example,peroxide-curing, sulfur-curing, high-energy radiation, and combinationsthereof. Preferably, the rubber composition contains a free-radicalinitiator selected from organic peroxides, high energy radiation sourcescapable of generating free-radicals, and combinations thereof. In onepreferred version, the rubber composition is peroxide-cured. Suitableorganic peroxides include, but are not limited to, dicumyl peroxide;n-butyl-4,4-di(t-butylperoxy) valerate;1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane;2,5-dimethyl-2,5-di(t-butylperoxy) hexane; di-t-butyl peroxide;di-t-amyl peroxide; t-butyl peroxide; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3;di(2-t-butyl-peroxyisopropyl)benzene; dilauroyl peroxide; dibenzoylperoxide; t-butyl hydroperoxide; and combinations thereof. In aparticular embodiment, the free radical initiator is dicumyl peroxide,including, but not limited to Perkadox® BC, commercially available fromAkzo Nobel. Peroxide free-radical initiators are generally present inthe rubber composition in an amount of at least 0.05 parts by weight per100 parts of the total rubber, or an amount within the range having alower limit of 0.05 parts or 0.1 parts or 1 part or 1.25 parts or 1.5parts or 2.5 parts or 5 parts by weight per 100 parts of the totalrubbers, and an upper limit of 2.5 parts or 3 parts or 5 parts or 6parts or 10 parts or 15 parts by weight per 100 parts of the totalrubber. Concentrations are in parts per hundred (phr) unless otherwiseindicated. As used herein, the term, “parts per hundred,” also known as“phr” or “pph” is defined as the number of parts by weight of aparticular component present in a mixture, relative to 100 parts byweight of the polymer component. Mathematically, this can be expressedas the weight of an ingredient divided by the total weight of thepolymer, multiplied by a factor of 100.

The rubber compositions may further include a reactive cross-linkingco-agent. Suitable co-agents include, but are not limited to, metalsalts of unsaturated carboxylic acids having from 3 to 8 carbon atoms;unsaturated vinyl compounds and polyfunctional monomers (e.g.,trimethylolpropane trimethacrylate); phenylene bismaleimide; andcombinations thereof. Particular examples of suitable metal saltsinclude, but are not limited to, one or more metal salts of acrylates,diacrylates, methacrylates, and dimethacrylates, wherein the metal isselected from magnesium, calcium, zinc, aluminum, lithium, and nickel.In a particular embodiment, the co-agent is selected from zinc salts ofacrylates, diacrylates, methacrylates, and dimethacrylates. In anotherparticular embodiment, the agent is zinc diacrylate (ZDA). When theco-agent is zinc diacrylate and/or zinc dimethacrylate, the co-agent istypically included in the rubber composition in an amount within therange having a lower limit of 1 or 5 or 10 or 15 or 19 or 20 parts byweight per 100 parts of the total rubber, and an upper limit of 24 or 25or 30 or 35 or 40 or 45 or 50 or 60 parts by weight per 100 parts of thebase rubber.

Radical scavengers such as a halogenated organosulfur, organicdisulfide, or inorganic disulfide compounds may be added to the rubbercomposition. These compounds also may function as “soft and fastagents.” As used herein, “soft and fast agent” means any compound or ablend thereof that is capable of making a core: 1) softer (having alower compression) at a constant “coefficient of restitution” (COR);and/or 2) faster (having a higher COR at equal compression), whencompared to a core equivalently prepared without a soft and fast agent.Preferred halogenated organosulfur compounds include, but are notlimited to, pentachlorothiophenol (PCTP) and salts of PCTP such as zincpentachlorothiophenol (ZnPCTP). Using PCTP and ZnPCTP in golf ball innercores helps produce softer and faster inner cores. The PCTP and ZnPCTPcompounds help increase the resiliency and the coefficient ofrestitution of the core. In a particular embodiment, the soft and fastagent is selected from ZnPCTP, PCTP, ditolyl disulfide, diphenyldisulfide, dixylyl disulfide, 2-nitroresorcinol, and combinationsthereof.

In addition, the rubber compositions may include antioxidants. Also,processing aids such as high molecular weight organic acids and saltsthereof may be added to the composition. Other ingredients such asaccelerators, dyes and pigments, wetting agents, surfactants,plasticizers, coloring agents, fluorescent agents, stabilizers,softening agents, impact modifiers, antiozonants, as well as otheradditives known in the art may be added to the rubber composition. Therubber composition also may include filler(s) such as materials selectedfrom carbon black, clay and nanoclay particles as discussed above, talc(e.g., Luzenac HAR® high aspect ratio talcs, commercially available fromLuzenac America, Inc.), glass (e.g., glass flake, milled glass, andmicroglass), mica and mica-based pigments (e.g., Iriodin® pearl lusterpigments, commercially available from The Merck Group), and combinationsthereof. Metal fillers such as, for example, particulate; powders;flakes; and fibers of copper, steel, brass, tungsten, titanium,aluminum, magnesium, molybdenum, cobalt, nickel, iron, lead, tin, zinc,barium, bismuth, bronze, silver, gold, and platinum, and alloys andcombinations thereof also may be added to the rubber composition toadjust the specific gravity of the composition as needed. As discussedabove, the inner core layer preferably has a specific gravity (density)greater than the inner core layer's specific gravity. Thus, metal orother fillers may be added to the polybutadiene rubber composition (orother thermoset material) used to form the inner core layer in asufficient amount so the specific gravity of the inner core remainsgreater than the specific gravity of the outer core.

Examples of commercially-available polybutadiene rubbers that can beused in accordance with this invention, include, but are not limited to,BR 01 and BR 1220, available from BST Elastomers of Bangkok, Thailand;SE BR 1220LA and SE BR1203, available from DOW Chemical Co of Midland,Mich.; BUDENE 1207, 1207s, 1208, and 1280 available from Goodyear, Incof Akron, Ohio; BR 01, 51 and 730, available from Japan Synthetic Rubber(JSR) of Tokyo, Japan; BUNA CB 21, CB 22, CB 23, CB 24, CB 25, CB 29MES, CB 60, CB Nd 60, CB 55 NF, CB 70 B, CB KA 8967, and CB 1221,available from Lanxess Corp. of Pittsburgh. Pa.; BR1208, available fromLG Chemical of Seoul, South Korea; UBEPOL BR130B, BR150, BR150B, BR150L,BR230, BR360L, BR710, and VCR617, available from UBE Industries, Ltd. ofTokyo, Japan; EUROPRENE NEOCIS BR 60, INTENE 60 AF and P30AF, andEUROPRENE BR HV80, available from Polimeri Europa of Rome, Italy; AFDENE50 and NEODENE BR40, BR45, BR50 and BR60, available from Karbochem (PTY)Ltd. of Bruma, South Africa; KBR 01, NdBr 40, NdBR-45, NdBr 60, KBR710S, KBR 710H, and KBR 750, available from Kumho Petrochemical Co.,Ltd. Of Seoul, South Korea; DIENE 55NF, 70AC, and 320 AC, available fromFirestone Polymers of Akron, Ohio; and PBR-Nd Group II and Group III,available from Nizhnekamskneftekhim, Inc. of Nizhnekamsk, TartarstanRepublic.

The polybutadiene rubber is used in an amount of at least about 5% byweight based on total weight of composition and is generally present inan amount of about 5% to about 100%, or an amount within a range havinga lower limit of 5% or 10% or 20% or 30% or 40% or 50% and an upperlimit of 55% or 60% or 70% or 80% or 90% or 95% or 100%. Preferably, theconcentration of polybutadiene rubber is about 40 to about 95 weightpercent. If desirable, lesser amounts of other thermoset materials maybe incorporated into the base rubber. Such materials include the rubbersdiscussed above, for example, cis-polyisoprene, trans-polyisoprene,balata, polychloroprene, polynorbornene, polyoctenamer, polypentenamer,butyl rubber, EPR, EPDM, styrene-butadiene, and the like.

As discussed above, in one preferred embodiment, a thermoset rubbercomposition is used to form the inner core. In alternative embodiments,the inner core layer is made from a thermoplastic material, for example,an ionomer composition.

Suitable ionomer compositions include partially-neutralized ionomers andhighly-neutralized ionomers (HNPs), including ionomers formed fromblends of two or more partially-neutralized ionomers, blends of two ormore highly-neutralized ionomers, and blends of one or morepartially-neutralized ionomers with one or more highly-neutralizedionomers. For purposes of the present disclosure, “HNP” refers to anacid copolymer after at least 70% of all acid groups present in thecomposition are neutralized.

Preferred ionomers are salts of O/X- and O/X/Y-type acid copolymers,wherein O is an α-olefin, X is a C₃-C₈α,β-ethylenically unsaturatedcarboxylic acid, and Y is a softening monomer. O is preferably selectedfrom ethylene and propylene. X is preferably selected from methacrylicacid, acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid.Methacrylic acid and acrylic acid are particularly preferred. Y ispreferably selected from (meth) acrylate and alkyl (meth) acrylateswherein the alkyl groups have from 1 to 8 carbon atoms, including, butnot limited to, n-butyl (meth) acrylate, isobutyl (meth) acrylate,methyl (meth) acrylate, and ethyl (meth) acrylate.

Preferred O/X and O/X/Y-type copolymers include, without limitation,ethylene acid copolymers, such as ethylene/(meth)acrylic acid,ethylene/(meth)acrylic acid/maleic anhydride, ethylene/(meth)acrylicacid/maleic acid mono-ester, ethylene/maleic acid, ethylene/maleic acidmono-ester, ethylene/(meth)acrylic acid/n-butyl (meth)acrylate,ethylene/(meth)acrylic acid/iso-butyl (meth)acrylate,ethylene/(meth)acrylic acid/methyl (meth)acrylate,ethylene/(meth)acrylic acid/ethyl (meth)acrylate terpolymers, and thelike. The term, “copolymer,” as used herein, includes polymers havingtwo types of monomers, those having three types of monomers, and thosehaving more than three types of monomers. Preferred α, β-ethylenicallyunsaturated mono- or dicarboxylic acids are (meth) acrylic acid,ethacrylic acid, maleic acid, crotonic acid, fumaric acid, itaconicacid. (Meth) acrylic acid is most preferred. As used herein, “(meth)acrylic acid” means methacrylic acid and/or acrylic acid. Likewise,“(meth) acrylate” means methacrylate and/or acrylate.

In a particularly preferred version, highly neutralized E/X- andE/X/Y-type acid copolymers, wherein E is ethylene, X is a C₃-C₈α,β-ethylenically unsaturated carboxylic acid, and Y is a softeningmonomer are used. X is preferably selected from methacrylic acid,acrylic acid, ethacrylic acid, crotonic acid, and itaconic acid.Methacrylic acid and acrylic acid are particularly preferred. Y ispreferably an acrylate selected from alkyl acrylates and aryl acrylatesand preferably selected from (meth) acrylate and alkyl (meth) acrylateswherein the alkyl groups have from 1 to 8 carbon atoms, including, butnot limited to, n-butyl (meth) acrylate, isobutyl (meth) acrylate,methyl (meth) acrylate, and ethyl (meth) acrylate. Preferred E/X/Y-typecopolymers are those wherein X is (meth) acrylic acid and/or Y isselected from (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth)acrylate, methyl (meth) acrylate, and ethyl (meth) acrylate. Morepreferred E/X/Y-type copolymers are ethylene/(meth) acrylic acid/n-butylacrylate, ethylene/(meth) acrylic acid/methyl acrylate, andethylene/(meth) acrylic acid/ethyl acrylate.

The amount of ethylene in the acid copolymer is typically at least 15wt. %, preferably at least 25 wt. %, more preferably least 40 wt. %, andeven more preferably at least 60 wt. %, based on total weight of thecopolymer. The amount of C₃ to C₈ α,β-ethylenically unsaturated mono- ordicarboxylic acid in the acid copolymer is typically from 1 wt. % to 35wt. %, preferably from 5 wt. % to 30 wt. %, more preferably from 5 wt. %to 25 wt. %, and even more preferably from 5 wt. % to 20 wt. %, based ontotal weight of the copolymer. The amount of optional softeningcomonomer in the acid copolymer is typically from 0 wt. % to 50 wt. %,preferably from 5 wt. % to 40 wt. %, more preferably from 10 wt. % to 35wt. %, and even more preferably from 20 wt. % to 30 wt. %, based ontotal weight of the copolymer. “Low acid” and “high acid” ionomericpolymers, as well as blends of such ionomers, may be used. In general,low acid ionomers are considered to be those containing 16 wt. % or lessof acid moieties, whereas high acid ionomers are considered to be thosecontaining greater than 16 wt. % of acid moieties.

The various O/X, E/X, O/X/Y, and E/X/Y-type copolymers are at leastpartially neutralized with a cation source, optionally in the presenceof a high molecular weight organic acid, such as those disclosed inRajagopalan et al., U.S. Pat. No. 6,756,436, the entire disclosure ofwhich is hereby incorporated herein by reference. The acid copolymer canbe reacted with the optional high molecular weight organic acid and thecation source simultaneously, or prior to the addition of the cationsource. Suitable cation sources include, but are not limited to, metalion sources, such as compounds of alkali metals, alkaline earth metals,transition metals, and rare earth elements; ammonium salts and monoaminesalts; and combinations thereof. Preferred cation sources are compoundsof magnesium, sodium, potassium, cesium, calcium, barium, manganese,copper, zinc, lead, tin, aluminum, nickel, chromium, lithium, and rareearth metals. The amount of cation used in the composition is readilydetermined based on desired level of neutralization. As discussed above,for HNP compositions, the acid groups are neutralized to 70% or greater,preferably 70 to 100%, more preferably 90 to 100%. In one embodiment, anexcess amount of neutralizing agent, that is, an amount greater than thestoichiometric amount needed to neutralize the acid groups, may be used.That is, the acid groups may be neutralized to 100% or greater, forexample 110% or 120% or greater. In other embodiments,partially-neutralized compositions are prepared, wherein 10% or greater,normally 30% or greater of the acid groups are neutralized. Whenaluminum is used as the cation source, it is preferably used at lowlevels with another cation such as zinc, sodium, or lithium, sincealuminum has a dramatic effect on melt flow reduction and cannot be usedalone at high levels. For example, aluminum is used to neutralize about10% of the acid groups and sodium is added to neutralize an additional90% of the acid groups.

“Ionic plasticizers” such as organic acids or salts of organic acids,particularly fatty acids, may be added to the ionomer resin. Such ionicplasticizers are used to make conventional ionomer composition moreprocessable as described in the above-mentioned U.S. Pat. No. 6,756,436.In the present invention such ionic plasticizers are optional. In onepreferred embodiment, a thermoplastic ionomer composition is made byneutralizing about 70 wt % or more of the acid groups without the use ofany ionic plasticizer. On the other hand, in some instances, it may bedesirable to add a small amount of ionic plasticizer, provided that itdoes not adversely affect the heat-resistance properties of thecomposition. For example, the ionic plasticizer may be added in anamount of about 10 to about 60 weight percent (wt. %) of thecomposition, more preferably 30 to 55 wt. %.

The organic acids may be aliphatic, mono- or multi-functional(saturated, unsaturated, or multi-unsaturated) organic acids. Salts ofthese organic acids may also be employed. Suitable fatty acid saltsinclude, for example, metal stearates, laureates, oleates, palmitates,pelargonates, and the like. For example, fatty acid salts such as zincstearate, calcium stearate, magnesium stearate, barium stearate, and thelike can be used. The salts of fatty acids are generally fatty acidsneutralized with metal ions. The metal cation salts provide the cationscapable of neutralizing (at varying levels) the carboxylic acid groupsof the fatty acids. Examples include the sulfate, carbonate, acetate andhydroxide salts of metals such as barium, lithium, sodium, zinc,bismuth, chromium, cobalt, copper, potassium, strontium, titanium,tungsten, magnesium, cesium, iron, nickel, silver, aluminum, tin, orcalcium, and blends thereof. It is preferred the organic acids and saltsbe relatively non-migratory (they do not bloom to the surface of thepolymer under ambient temperatures) and non-volatile (they do notvolatilize at temperatures required for melt-blending).

Other suitable thermoplastic polymers that may be used to form the innercore layer include, but are not limited to, the following polymers(including homopolymers, copolymers, and derivatives thereof.)

(a) polyesters, particularly those modified with a compatibilizing groupsuch as sulfonate or phosphonate, including modified poly(ethyleneterephthalate), modified poly(butylene terephthalate), modifiedpoly(propylene terephthalate), modified poly(trimethyleneterephthalate), modified poly(ethylene naphthenate), and those disclosedin U.S. Pat. Nos. 6,353,050, 6,274,298, and 6,001,930, the entiredisclosures of which are hereby incorporated herein by reference, andblends of two or more thereof;

(b) polyamides, polyamide-ethers, and polyamide-esters, and thosedisclosed in U.S. Pat. Nos. 6,187,864, 6,001,930, and 5,981,654, theentire disclosures of which are hereby incorporated herein by reference,and blends of two or more thereof;

(c) polyurethanes, polyureas, polyurethane-polyurea hybrids, and blendsof two or more thereof;

(d) fluoropolymers, such as those disclosed in U.S. Pat. Nos. 5,691,066,6,747,110 and 7,009,002, the entire disclosures of which are herebyincorporated herein by reference, and blends of two or more thereof;

(e) polystyrenes, such as poly(styrene-co-maleic anhydride),acrylonitrile-butadiene-styrene, poly(styrene sulfonate), polyethylenestyrene, and blends of two or more thereof;

(f) polyvinyl chlorides and grafted polyvinyl chlorides, and blends oftwo or more thereof;

(g) polycarbonates, blends ofpolycarbonate/acrylonitrile-butadiene-styrene, blends ofpolycarbonate/polyurethane, blends of polycarbonate/polyester, andblends of two or more thereof;

(h) polyethers, such as polyarylene ethers, polyphenylene oxides, blockcopolymers of alkenyl aromatics with vinyl aromatics and polyamicesters,and blends of two or more thereof;

(i) polyimides, polyetherketones, polyamideimides, and blends of two ormore thereof; and

(j) polycarbonate/polyester copolymers and blends.

It also is recognized that thermoplastic materials can be “converted”into thermoset materials by cross-linking the polymer chains so theyform a network structure, and such cross-linked thermoplastic materialsmay be used to form the inner cover layers in accordance with thisinvention. For example, thermoplastic polyolefins such as linear lowdensity polyethylene (LLDPE), low density polyethylene (LDPE), and highdensity polyethylene (HDPE) may be cross-linked to form bonds betweenthe polymer chains. The cross-linked thermoplastic material typicallyhas improved physical properties and strength over non-cross-linkedthermoplastics, particularly at temperatures above the crystallinemelting point. Preferably a partially or fully-neutralized ionomer, asdescribed above, is covalently cross-linked to render it into athermoset composition (that is, it contains at least some level ofcovalent, irreversable cross-links). Thermoplastic polyurethanes andpolyureas also may be converted into thermoset materials in accordancewith the present invention.

Modifications in the thermoplastic polymeric structure of thermoplasticscan be induced by a number of methods, including exposing thethermoplastic material to high-energy radiation or through a chemicalprocess using peroxide. Radiation sources include, but are not limitedto, gamma-rays, electrons, neutrons, protons, x-rays, helium nuclei, orthe like. Gamma radiation, typically using radioactive cobalt atoms andallows for considerable depth of treatment, if necessary. For corelayers requiring lower depth of penetration, electron-beam acceleratorsor UV and IR light sources can be used. Useful UV and IR irradiationmethods are disclosed in U.S. Pat. Nos. 6,855,070 and 7,198,576, whichare incorporated herein by reference. The thermoplastic core layers maybe irradiated at dosages greater than 0.05 Mrd, preferably ranging from1 Mrd to 20 Mrd, more preferably from 2 Mrd to 15 Mrd, and mostpreferably from 4 Mrd to 10 Mrd. In one preferred embodiment, the coresare irradiated at a dosage from 5 Mrd to 8 Mrd and in another preferredembodiment, the cores are irradiated with a dosage from 0.05 Mrd to 3Mrd, more preferably 0.05 Mrd to 1.5 Mrd.

The cross-linked thermoplastic material may be created by exposing thethermoplastic to: 1) a high-energy radiation treatment, such as electronbeam or gamma radiation, such as disclosed in U.S. Pat. No. 5,891,973,which is incorporated by reference herein, 2) lower energy radiation,such as ultra-violet (UV) or infra-red (IR) radiation; 3) a solutiontreatment, such as an isocyanate or a silane; 4) incorporation ofadditional free radical initiator groups in the thermoplastic prior tomolding; and/or 5) chemical modification, such as esterification orsaponification, to name a few.

Outer Core Composition

In the present invention, the inner core (center) preferably comprises anon-foamed thermoplastic or thermoset polymer composition. Meanwhile,the surrounding outer core layer preferably comprises a foamedcomposition. The foam may have an open or closed cellular structure orcombinations thereof and the foam structure may range from a relativelyrigid foam to a very flexible foam. In one preferred embodiment, theouter core comprises a relatively soft foam composition.

In general, foam compositions are made by forming gas bubbles in apolymer mixture using a foaming (blowing) agent. As the bubbles form,the mixture expands and forms a foam composition that can be molded intoan end-use product having either an open or closed cellular structure.Flexible foams generally have an open cell structure, where the cellswalls are incomplete and contain small holes through which liquid andair can permeate. Such flexible foams are used traditionally forautomobile seats, cushioning, mattresses, and the like. Rigid foamsgenerally have a closed cell structure, where the cell walls arecontinuous and complete, and are used for used traditionally forautomobile panels and parts, building insulation and the like. Manyfoams contain both open and closed cells. It also is possible toformulate flexible foams having a closed cell structure and likewise toformulate rigid foams having an open cell structure.

A wide variety of thermoplastic and thermoset materials may be used informing the foam composition of this invention including, for example,polyurethanes; polyureas; copolymers, blends and hybrids of polyurethaneand polyurea; olefin-based copolymer ionomer resins (for example,Surlyn® ionomer resins and DuPont HPF® 1000 and HPF® 2000, commerciallyavailable from DuPont; Iotek® ionomers, commercially available fromExxonMobil Chemical Company; Amplify® ionomers onomers of ethyleneacrylic acid copolymers, commercially available from Dow ChemicalCompany; and Clarix® ionomer resins, commercially available from A.Schulman Inc.); polyethylene, including, for example, low densitypolyethylene, linear low density polyethylene, and high densitypolyethylene; polypropylene; rubber-toughened olefin polymers; acidcopolymers, for example, poly(meth)acrylic acid, which do not becomepart of an ionomeric copolymer; plastomers; flexomers;styrene/butadiene/styrene block copolymers;styrene/ethylene-butylene/styrene block copolymers; dynamicallyvulcanized elastomers; copolymers of ethylene and vinyl acetates;copolymers of ethylene and methyl acrylates; polyvinyl chloride resins;polyamides, poly(amide-ester) elastomers, and graft copolymers ofionomer and polyamide including, for example, Pebax® thermoplasticpolyether block amides, commercially available from Arkema Inc;cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to make a golf ball havinggood playing performance properties as discussed further below. By theterm, “hybrids of polyurethane and polyurea,” it is meant to includecopolymers and blends thereof.

Basically, polyurethane compositions contain urethane linkages formed bythe reaction of a multi-functional isocyanate containing two or more NCOgroups with a polyol having two or more hydroxyl groups (OH—OH)sometimes in the presence of a catalyst and other additives. Generally,polyurethanes can be produced in a single-step reaction (one-shot) or ina two-step reaction via a prepolymer or quasi-prepolymer. In theone-shot method, all of the components are combined at once, that is,all of the raw ingredients are added to a reaction vessel, and thereaction is allowed to take place. In the prepolymer method, an excessof polyisocyanate is first reacted with some amount of a polyol to formthe prepolymer which contains reactive NCO groups. This prepolymer isthen reacted again with a chain extender or curing agent polyol to formthe final polyurethane. Polyurea compositions, which are distinct fromthe above-described polyurethanes, also can be formed. In general,polyurea compositions contain urea linkages formed by reacting anisocyanate group (—N═C═O) with an amine group (NH or NH₂). Polyureas canbe produced in similar fashion to polyurethanes by either a one shot orprepolymer method. In forming a polyurea polymer, the polyol would besubstituted with a suitable polyamine. Hybrid compositions containingurethane and urea linkages also may be produced. For example, whenpolyurethane prepolymer is reacted with amine-terminated curing agentsduring the chain-extending step, any excess isocyanate groups in theprepolymer will react with the amine groups in the curing agent. Theresulting polyurethane-urea composition contains urethane and urealinkages and may be referred to as a hybrid. In another example, ahybrid composition may be produced when a polyurea prepolymer is reactedwith a hydroxyl-terminated curing agent. A wide variety of isocyanates,polyols, polyamines, and curing agents can be used to form thepolyurethane and polyurea compositions as discussed further below.

To prepare the foamed polyurethane, polyurea, or other polymercomposition, a foaming agent is introduced into the polymer formulation.In general, there are two types of foaming agents: physical foamingagents and chemical foaming agents.

Physical Foaming Agents.

These foaming agents typically are gasses that are introduced under highpressure directly into the polymer composition. Chlorofluorocarbons(CFCs) and partially halogenated chlorofluorocarbons are effective, butthese compounds are banned in many countries because of theirenvironmental side effects. Alternatively, aliphatic and cyclichydrocarbon gasses such as isobutene and pentane may be used. Inertgasses, such as carbon dioxide and nitrogen, also are suitable. Withphysical foaming agents, the isocyanate and polyol compounds react toform polyurethane linkages and the reaction generates heat. Foam cellsare generated and as the foaming agent vaporizes, the gas becomestrapped in the cells of the foam.

Chemical Foaming Agents.

These foaming agents typically are in the form of powder, pellets, orliquids and they are added to the composition, where they decompose orreact during heating and generate gaseous by-products (for example,nitrogen or carbon dioxide). The gas is dispersed and trapped throughoutthe composition and foams it. For example, water may be used as thefoaming agent. Air bubbles are introduced into the mixture of theisocyanate and polyol compounds and water by high-speed mixingequipment. As discussed in more detail further below, the isocyanatesreact with the water to generate carbon dioxide which fills and expandsthe cells created during the mixing process.

Preferably, a chemical foaming agent is used to prepare the foamcompositions of this invention. Chemical blowing agents may beinorganic, such as ammonium carbonate and carbonates of alkalai metals,or may be organic, such as azo and diazo compounds, such asnitrogen-based azo compounds. Suitable azo compounds include, but arenot limited to, 2,2′-azobis(2-cyanobutane),2,2′-azobis(methylbutyronitrile), azodicarbonamide, p,p′-oxybis(benzenesulfonyl hydrazide), p-toluene sulfonyl semicarbazide, p-toluenesulfonyl hydrazide. Other foaming agents include any of the Celogens®sold by Crompton Chemical Corporation, and nitroso compounds,sulfonylhydrazides, azides of organic acids and their analogs,triazines, tri- and tetrazole derivatives, sulfonyl semicarbazides, ureaderivatives, guanidine derivatives, and esters such as alkoxyboroxines.Also, foaming agents that liberate gasses as a result of chemicalinteraction between components such as mixtures of acids and metals,mixtures of organic acids and inorganic carbonates, mixtures of nitrilesand ammonium salts, and the hydrolytic decomposition of urea may beused. Water is a preferred foaming agent. When added to the polyurethaneformulation, water will react with the isocyanate groups and formcarbamic acid intermediates. The carbamic acids readily decarboxylate toform an amine and carbon dioxide. The newly formed amine can thenfurther react with other isocyanate groups to form urea linkages and thecarbon dioxide forms the bubbles to produce the foam.

During the decomposition reaction of certain chemical foaming agents,more heat and energy is released than is needed for the reaction. Oncethe decomposition has started, it continues for a relatively long timeperiod. If these foaming agents are used, longer cooling periods aregenerally required. Hydrazide and azo-based compounds often are used asexothermic foaming agents. On the other hand, endothermic foaming agentsneed energy for decomposition. Thus, the release of the gasses quicklystops after the supply of heat to the composition has been terminated.If the composition is produced using these foaming agents, shortercooling periods are needed. Bicarbonate and citric acid-based foamingagents can be used as exothermic foaming agents.

Other suitable foaming agents include expandable gas-containingmicrospheres. Exemplary microspheres consist of an acrylonitrile polymershell encapsulating a volatile gas, such as isopentane gas. This gas iscontained within the sphere as a blowing agent. In their unexpandedstate, the diameter of these hollow spheres range from 10 to 17 μm andhave a true density of 1000 to 1300 kg/m³. When heated, the gas insidethe shell increases its pressure and the thermoplastic shell softens,resulting in a dramatic increase of the volume of the microspheres.Fully expanded, the volume of the microspheres will increase more than40 times (typical diameter values would be an increase from 10 to 40μm), resulting in a true density below 30 kg/m³ (0.25 lbs/gallon).Typical expansion temperatures range from 80-190° C. (176-374° F.). Suchexpandable microspheres are commercially available as Expancel® fromExpancel of Sweden or Akzo Nobel.

As an alternative to chemical and physical foaming agents or in additionto such foaming agents, as described above, other types of fillers thatlower the specific gravity of the composition can be used in accordancewith this invention. For example, polymeric, ceramic, and glass unfilledmicrospheres having a density of 0.1 to 1.0 g/cc and an average particlesize of 10 to 250 microns can be used to help lower specific gravity ofthe composition and achieve the desired density and physical properties.However, it is still preferred that the density of the foamed outer corelayer be less than the density of the inner core layer.

Additionally, BASF polyurethane materials sold under the trade nameCellasto® and Elastocell®, microcellular polyurethanes, Elastopor® Hthat is a closed-cell polyurethane rigid foam, Elastoflex® W flexiblefoam systems, Elastoflex®E semiflexible foam systems, Elastofoam®flexible integrally-skinning systems, Elastolit®D/K/R integral rigidfoams, Elastopan®S, Elastollan® thermoplastic polyurethane elastomers(TPUs), and the like may be used in accordance with the presentinvention. Furthermore, BASF closed-cell, pre-expanded thermoplastic(TPU) polyurethane foam, available under the mark, Infinergy™ also maybe used to form the foam centers of the golf balls in accordance withthis invention. It also is believed these foam materials would be usefulin forming non-center foamed layers in a variety of golf ballconstructions. Such closed-cell, pre-expanded TPU foams are described inPrissok et al., US Patent Applications 2012/0329892; 2012/0297513; and2013/0227861; and U.S. Pat. No. 8,282,851 the disclosures of which arehereby incorporated by reference. Bayer also produces a variety ofmaterials sold as Texin® TPUs, Baytec® and Vulkollan® elastomers,Baymer® rigid foams, Baydur® integral skinning foams, Bayfit® flexiblefoams available as castable, RIM grades, sprayable, and the like thatmay be used. Additional foam materials that may be used herein includepolyisocyanurate foams and a variety of “thermoplastic” foams, which maybe cross-linked to varying extents using free-radical (for example,peroxide) or radiation cross-linking (for example, UV, IR, Gamma, EBirradiation). Also, foams may be prepared from polybutadiene,polystyrene, polyolefin (including metallocene and other single sitecatalyzed polymers), ethylene vinyl acetate (EVA), acrylate copolymers,such as EMA, EBA, Nucrel®-type acid co and terpolymers, ethylenepropylene rubber (such as EPR, EPDM, and any ethylene copolymers),styrene-butadiene, and SEBS (any Kraton-type), PVC, PVDC, CPE(chlorinated polyethylene). Epoxy foams, urea-formaldehyde foams, latexfoams and sponge, silicone foams, fluoropolymer foams and syntacticfoams (hollow sphere filled) also may be used. In particular, siliconefoams may be used. For example, the inner core (center) may be made of asilicone foam rubber and the surrounding outer core layer may be made ofa non-foamed thermoset or thermoplastic composition. The silicone foamrubber composition has good thermal stability. Thus, the thermoset orthermoplastic composition may be molded more effectively over the innercore, and the chemical and physical properties of the inner core willnot degrade substantially

In addition to the polymer and foaming agent, the foam composition alsomay include other ingredients such as, for example, fillers,cross-linking agents, chain extenders, surfactants, dyes and pigments,coloring agents, fluorescent agents, adsorbents, stabilizers, softeningagents, impact modifiers, antioxidants, antiozonants, and the like. Theformulations used to prepare the polyurethane foam compositions of thisinvention preferably contain a polyol, polyisocyanate, water, an amineor hydroxyl curing agent, surfactant, and a catalyst as describedfurther below.

Fillers.

The polyurethane foam composition may contain fillers such as, forexample, mineral filler particulate. Suitable mineral fillerparticulates include compounds such as zinc oxide, limestone, silica,mica, barytes, lithopone, zinc sulfide, talc, calcium carbonate,magnesium carbonate, clays, powdered metals and alloys such as bismuth,brass, bronze, cobalt, copper, iron, nickel, tungsten, aluminum, tin,precipitated hydrated silica, fumed silica, mica, calcium metasilicate,barium sulfate, zinc sulfide, lithopone, silicates, silicon carbide,diatomaceous earth, carbonates such as calcium or magnesium or bariumcarbonate, sulfates such as calcium or magnesium or barium sulfate.Adding fillers to the foam composition provides many benefits includinghelping improve the stiffness and strength of the composition. Themineral fillers tend to help decrease the size of the foam cells andincrease cell density. The mineral fillers also tend to help improve thephysical properties of the foam such as hardness, compression set, andtensile strength. However, in the present invention, it is important theconcentration of fillers in the foam composition be not so high as tosubstantially increase the specific gravity (density) of thecomposition. Particularly, the specific gravity of the outer core ismaintained such that is less than the specific gravity of the innercore. The foam composition may contain some fillers; provided however,the specific gravity of the foam composition (inner core) is kept lessthan the composition of the inner core. In one embodiment, the foamcomposition is substantially free of fillers. In another embodiment, thefoam composition contains no fillers and consists of a mixture ofpolyisocyanate, polyol, and curing agent, surfactant, catalyst, andwater, the water being added in sufficient amount to cause the mixtureto foam as discussed above.

If filler is added to the foam composition, clay particulate fillers areparticularly suitable. The clay particulate fillers include Garamite®mixed mineral thixotropes and Cloisite® and Nanofil® nanoclays,commercially available from Southern Clay Products, Inc., and Nanomax®and Nanomer® nanoclays, commercially available from Nanocor, Inc may beused. Other nano-scale materials such as nanotubes and nanoflakes alsomay be used. Also, talc particulate (e.g., Luzenac HAR® high aspectratio talcs, commercially available from Luzenac America, Inc.), glass(e.g., glass flake, milled glass, and microglass), and combinationsthereof may be used. Metal oxide fillers have good heat-stability andmay be added including, for example, aluminum oxide, zinc oxide, tinoxide, barium sulfate, zinc sulfate, calcium oxide, calcium carbonate,zinc carbonate, barium carbonate, tungsten, tungsten carbide, and leadsilicate fillers. Other metal fillers such as, for example, particulate;powders; flakes; and fibers of copper, steel, brass, tungsten, titanium,aluminum, magnesium, molybdenum, cobalt, nickel, iron, lead, tin, zinc,barium, bismuth, bronze, silver, gold, and platinum, and alloys andcombinations thereof also may be added to the foam composition.

Surfactants.

The foam composition also may contain surfactants to stabilize the foamand help control the foam cell size and structure. In one preferredversion, the foam composition includes silicone surfactant. In general,the silicone surfactant helps regulate the foam cell size and stabilizesthe cell walls to prevent the cells from collapsing. As discussed above,the liquid reactants react to form the foam rapidly. The “liquid” foamdevelops into solid silicone foam in a relatively short period of time.If a silicone surfactant is not added, the gas-liquid interface betweenthe liquid reactants and expanding gas bubbles may not support thestress. As a result, the cell window can crack or rupture and there canbe cell wall drainage. In turn, the foam can collapse on itself. Addinga silicone surfactant helps create a surface tension gradient along thegas-liquid interface and helps reduce cell wall drainage. The siliconesurfactant has a relatively low surface tension and thus can lower thesurface tension of the foam. It is believed the silicone surfactantorients itself the foam cell walls and lowers the surface tension tocreate the surface tension gradient. Blowing efficiency and nucleationare supported by adding the silicone surfactant and thus more bubblesare created in the system. The silicone surfactant also helps create agreater number of smaller sized foam cells and increases the closed cellcontent of the foam due to the surfactant's lower surface tension. Thus,the cell structure in the foam is maintained as the as gas is preventedfrom diffusing out through the cell walls. Along with the decrease incell size, there is a decrease in thermal conductivity. The resultingfoam material also tends to have greater compression strength andmodulus. These improved physical properties may be due to the increasein closed cell content and smaller cell size.

Properties of Polyurethane Foams

The polyurethane foam compositions of this invention have numerouschemical and physical properties making them suitable for coreassemblies in golf balls. For example, there are properties relating tothe reaction of the isocyanate and polyol components and blowing agent,particularly “cream time,” “gel time,” “rise time,” “tack-free time,”and “free-rise density.” In general, cream time refers to the timeperiod from the point of mixing the raw ingredients together to thepoint where the mixture turns cloudy in appearance or changes color andbegins to rise from its initial stable state. Normally, the cream timeof the foam compositions of this invention is within the range of about20 to about 240 seconds. In general, gel time refers to the time periodfrom the point of mixing the raw ingredients together to the point wherethe expanded foam starts polymerizing/gelling. Rise time generallyrefers to the time period from the point of mixing the raw ingredientstogether to the point where the reacted foam has reached its largestvolume or maximum height. The rise time of the foam compositions of thisinvention typically is in the range of about 60 to about 360 seconds.Tack-free time generally refers to the time it takes for the reactedfoam to lose its tackiness, and the foam compositions of this inventionnormally have a tack-free time of about 60 to about 3600 seconds.Free-rise density refers to the density of the resulting foam when it isallowed to rise unrestricted without a cover or top being placed on themold.

The density of the foam is an important property and is defined as theweight per unit volume (typically, g/cm³) and can be measured per ASTMD-1622. The hardness, stiffness, and load-bearing capacity of the foamare independent of the foam's density, although foams having a highdensity typically have high hardness and stiffness. Normally, foamshaving higher densities have higher compression strength. Surprisingly,the foam compositions used to produce the inner core of the golf ballsper this invention have a relatively low density; however, the foams arenot necessarily soft and flexible, rather, they may be relatively firm,rigid, or semi-rigid depending upon the desired golf ball properties.Tensile strength, tear-resistance, and elongation generally refer to thefoam's ability to resist breaking or tearing, and these properties canbe measured per ASTM D-1623. The durability of foams is important,because introducing fillers and other additives into the foamcomposition can increase the tendency of the foam to break or tearapart. In general, the tensile strength of the foam compositions of thisinvention is in the range of about 20 to about 1000 psi (parallel to thefoam rise) and about 50 to about 1000 psi (perpendicular to the foamrise) as measured per ASTM D-1623 at 23° C. and 50% relative humidity(RH). Meanwhile, the flex modulus of the foams of this invention isgenerally in the range of about 5 to about 45 kPa as measured per ASTMD-790, and the foams generally have a compressive modulus of 200 to50,000 psi.

In another test, compression strength is measured on an Instron machineaccording to ASTM D-1621. The foam is cut into blocks and thecompression strength is measured as the force required for compressingthe block by 10%. In general, the compressive strength of the foamcompositions of this invention is in the range of about 100 to about1800 psi (parallel and perpendicular to the foam rise) as measured perASTM D-1621 at 23° C. and 50% relative humidity (RH). The test isconducted perpendicular to the rise of the foam or parallel to the riseof the foam. The Percentage (%) of Compression Set also can be used.This is a measure of the permanent deformation of a foam sample after ithas been compressed between two metal plates under controlled time andtemperature condition (standard—22 hours at 70° C. (158° F.)). The foamis compressed to a thickness given as a percentage of its originalthickness that remained “set.” Preferably, the Compression Set of thefoam is less than ten percent (10%), that is, the foam recovers to apoint of 90% or greater of its original thickness.

The foam compositions of this invention may be prepared using differentmethods. In one preferred embodiment, the method involves preparing acastable composition comprising a reactive mixture of a polyisocyanate,polyol, water, curing agent, surfactant, and catalyst. A motorized mixercan be used to mix the starting ingredients together and form a reactiveliquid mixture. Alternatively, the ingredients can be manually mixedtogether. An exothermic reaction occurs when the ingredients are mixedtogether and this continues as the reactive mixture is dispensed intothe mold cavities (otherwise referred to as half-molds or mold cups).

Polyisocyanates and Polyols for Making the Polyurethane Foams

As discussed above, in one preferred embodiment, a foamed polyurethanecomposition is used to form the inner core. In general, the polyurethanecompositions contain urethane linkages formed by reacting an isocyanategroup (—N═C═O) with a hydroxyl group (OH). The polyurethanes areproduced by the reaction of multi-functional isocyanates containing twoor more isocyanate groups with a polyol having two or more hydroxylgroups. The formulation may also contain a catalyst, surfactant, andother additives.

In particular, the foam inner core of this invention may be preparedfrom a composition comprising an aromatic polyurethane, which ispreferably formed by reacting an aromatic diisocyanate with a polyol.Suitable aromatic diisocyanates that may be used in accordance with thisinvention include, for example, toluene 2,4-diisocyanate (TDI), toluene2,6-diisocyanate (TDI), 4,4′-methylene diphenyl diisocyanate (MDI),2,4′-methylene diphenyl diisocyanate (MDI), polymeric methylene diphenyldiisocyanate (PMDI), p-phenylene diisocyanate (PPDI), m-phenylenediisocyanate (PDI), naphthalene 1,5-diisocyanate (NDI), naphthalene2,4-diisocyanate (NDI), p-xylene diisocyanate (XDI), and homopolymersand copolymers and blends thereof. The aromatic isocyanates are able toreact with the hydroxyl or amine compounds and form a durable and toughpolymer having a high melting point. The resulting polyurethanegenerally has good mechanical strength and tear-resistance.

Alternatively, the foamed composition of the inner core may be preparedfrom a composition comprising aliphatic polyurethane, which ispreferably formed by reacting an aliphatic diisocyanate with a polyol.Suitable aliphatic diisocyanates that may be used in accordance withthis invention include, for example, isophorone diisocyanate (IPDI),1,6-hexamethylene diisocyanate (HDI), 4,4′-dicyclohexylmethanediisocyanate (“H₁₂ MDI”), meta-tetramethylxylyene diisocyanate (TMXDI),trans-cyclohexane diisocyanate (CHDI),1,3-bis(isocyanatomethyl)cyclohexane;1,4-bis(isocyanatomethyl)cyclohexane; and homopolymers and copolymersand blends thereof. The resulting polyurethane generally has good lightand thermal stability. Preferred polyfunctional isocyanates include4,4′-methylene diphenyl diisocyanate (MDI), 2,4′-methylene diphenyldiisocyanate (MDI), and polymeric MDI having a functionality in therange of 2.0 to 3.5 and more preferably 2.2 to 2.5.

Any suitable polyol may be used to react with the polyisocyanate inaccordance with this invention. Exemplary polyols include, but are notlimited to, polyether polyols, hydroxy-terminated polybutadiene(including partially/fully hydrogenated derivatives), polyester polyols,polycaprolactone polyols, and polycarbonate polyols. In one preferredembodiment, the polyol includes polyether polyol. Examples include, butare not limited to, polytetramethylene ether glycol (PTMEG),polyethylene propylene glycol, polyoxypropylene glycol, and mixturesthereof. The hydrocarbon chain can have saturated or unsaturated bondsand substituted or unsubstituted aromatic and cyclic groups. Preferably,the polyol of the present invention includes PTMEG.

As discussed further below, chain extenders (curing agents) are added tothe mixture to build-up the molecular weight of the polyurethanepolymer. In general, hydroxyl-terminated curing agents, amine-terminatedcuring agents, and mixtures thereof are used.

A catalyst may be employed to promote the reaction between theisocyanate and polyol compounds. Suitable catalysts include, but are notlimited to, bismuth catalyst; zinc octoate; tin catalysts such asbis-butyltin dilaurate, bis-butyltin diacetate, stannous octoate; tin(II) chloride, tin (IV) chloride, bis-butyltin dimethoxide,dimethyl-bis[1-oxonedecyl)oxy]stannane, di-n-octyltin bis-isooctylmercaptoacetate; amine catalysts such as triethylenediamine,triethylamine, tributylamine, 1,4-diaza(2,2,2)bicyclooctane,tetramethylbutane diamine, bis[2-dimethylaminoethyl]ether,N,N-dimethylaminopropylamine, N,N-dimethylcyclohexylamine,N,N,N′,N′,N″-pentamethyldiethylenetriamine, diethanolamine,dimethtlethanolamine, N-[2-(dimethylamino)ethyl]-N-methylethanolamine,N-ethylmorpholine, 3-dimethylamino-N,N-dimethylpropionamide, andN,N′,N″-dimethylaminopropylhexahydrotriazine; organic acids such asoleic acid and acetic acid; delayed catalysts; and mixtures thereof.Zirconium-based catalysts such as, for example, bis(2-dimethylaminoethyl) ether; mixtures of zinc complexes and amine compounds suchas KKAT™ XK 614, available from King Industries; and amine catalystssuch as Niax™ A-2 and A-33, available from Momentive SpecialtyChemicals, Inc. are particularly preferred. The catalyst is preferablyadded in an amount sufficient to catalyze the reaction of the componentsin the reactive mixture. In one embodiment, the catalyst is present inan amount from about 0.001 percent to about 1 percent, and preferably0.1 to 0.5 percent, by weight of the composition.

In one preferred embodiment, as described above, water is used as thefoaming agent—the water reacts with the polyisocyanate compound(s) andforms carbon dioxide gas which induces foaming of the mixture. Thereaction rate of the water and polyisocyanate compounds affects howquickly the foam is formed as measured per reaction profile propertiessuch as cream time, gel time, and rise time of the foam.

The hydroxyl chain-extending (curing) agents are preferably selectedfrom the group consisting of ethylene glycol; diethylene glycol;polyethylene glycol; propylene glycol; 2-methyl-1,3-propanediol;2-methyl-1,4-butanediol; monoethanolamine; diethanolamine;triethanolamine; monoisopropanolamine; diisopropanolamine; dipropyleneglycol; polypropylene glycol; 1,2-butanediol; 1,3-butanediol;1,4-butanediol; 2,3-butanediol; 2,3-dimethyl-2,3-butanediol;trimethylolpropane; cyclohexyldimethylol; triisopropanolamine;N,N,N′,N′-tetra-(2-hydroxypropyl)-ethylene diamine; diethylene glycolbis-(aminopropyl) ether; 1,5-pentanediol; 1,6-hexanediol;1,3-bis-(2-hydroxyethoxy) cyclohexane; 1,4-cyclohexyldimethylol;1,3-bis-[2-(2-hydroxyethoxy) ethoxy]cyclohexane;1,3-bis-{2-[2-(2-hydroxyethoxy) ethoxy]ethoxy}cyclohexane;trimethylolpropane; polytetramethylene ether glycol (PTMEG), preferablyhaving a molecular weight from about 250 to about 3900; and mixturesthereof. Di, tri, and tetra-functional polycaprolactone diols such as,2-oxepanone polymer initiated with 1,4-butanediol,2-ethyl-2-(hydroxymethyl)-1,3-propanediol, or2,2-bis(hydroxymethyl)-1,3-propanediolsuch, may be used.

Suitable amine chain-extending (curing) agents that can be used inchain-extending the polyurethane prepolymer include, but are not limitedto, unsaturated diamines such as 4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-dianiline or “MDA”), m-phenylenediamine,p-phenylenediamine, 1,2- or 1,4-bis(sec-butylamino)benzene,3,5-diethyl-(2,4- or 2,6-) toluenediamine or “DETDA”,3,5-dimethylthio-(2,4- or 2,6-)toluenediamine, 3,5-diethylthio-(2,4- or2,6-)toluenediamine, 3,3′-dimethyl-4,4′-diamino-diphenylmethane,3,3′-diethyl-5,5′-dimethyl4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-ethyl-6-methyl-benezeneamine)),3,3′-dichloro-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2-chloroaniline) or “MOCA”),3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaniline),2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-diphenylmethane (i.e.,4,4′-methylene-bis(3-chloro-2,6-diethyleneaniline) or “MCDEA”),3,3T-diethyl-5,5′-dichloro-4,4′-diamino-diphenylmethane, or “MDEA”),3,3′-dichloro-2,2′,6,6′-tetraethyl-4,4′-diamino-diphenylmethane,3,3′-dichloro-4,4′-diamino-diphenylmethane,4,4′-methylene-bis(2,3-dichloroaniline) (i.e.,2,2′,3,3′-tetrachloro-4,4′-diamino-diphenylmethane or “MDCA”),4,4′-bis(sec-butylamino)-diphenylmethane,N,N′-dialkylamino-diphenylmethane,trimethyleneglycol-di(p-aminobenzoate),polyethyleneglycol-di(p-aminobenzoate),polytetramethyleneglycol-di(p-aminobenzoate); saturated diamines such asethylene diamine, 1,3-propylene diamine, 2-methyl-pentamethylenediamine, hexamethylene diamine, 2,2,4- and 2,4,4-trimethyl-1,6-hexanediamine, imino-bis(propylamine), imido-bis(propylamine),methylimino-bis(propylamine) (i.e.,N-(3-aminopropyl)-N-methyl-1,3-propanediamine),1,4-bis(3-aminopropoxy)butane (i.e.,3,3′-[1,4-butanediylbis-(oxy)bis]-1-propanamine),diethyleneglycol-bis(propylamine) (i.e.,diethyleneglycol-di(aminopropyl)ether),4,7,10-trioxatridecane-1,13-diamine, 1-methyl-2,6-diamino-cyclohexane,1,4-diamino-cyclohexane, poly(oxyethylene-oxypropylene) diamines, 1,3-or 1,4-bis(methylamino)-cyclohexane, isophorone diamine, 1,2- or1,4-bis(sec-butylamino)-cyclohexane, N,N′-diisopropyl-isophoronediamine, 4,4′-diamino-dicyclohexylmethane,3,3′-dimethyl-4,4′-diamino-dicyclohexylmethane,3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,N,N′-dialkylamino-dicyclohexylmethane, polyoxyethylene diamines,3,3′-diethyl-5,5′-dimethyl-4,4′-diamino-dicyclohexylmethane,polyoxypropylene diamines,3,3′-diethyl-5,5′-dichloro-4,4′-diamino-dicyclohexylmethane,polytetramethylene ether diamines, 3,3′,5,5‘-tetraethyl-4,4’-diamino-dicyclohexylmethane (i.e.,4,4′-methylene-bis(2,6-diethylaminocyclohexane)),3,3′-dichloro-4,4′-diamino-dicyclohexylmethane,2,2′-dichloro-3,3′,5,5′-tetraethyl-4,4′-diamino-dicyclohexylmethane,(ethylene oxide)-capped polyoxypropylene ether diamines,2,2′,3,3′-tetrachloro-4,4′-diamino-dicyclohexylmethane,4,4′-bis(sec-butylamino)-dicyclohexylmethane; triamines such asdiethylene triamine, dipropylene triamine, (propylene oxide)-basedtriamines (i.e., polyoxypropylene triamines),N-(2-aminoethyl)-1,3-propylenediamine (i.e., N₃-amine), glycerin-basedtriamines, (all saturated); tetramines such asN,N′-bis(3-aminopropyl)ethylene diamine (i.e., N₄-amine) (bothsaturated), triethylene tetramine; and other polyamines such astetraethylene pentamine (also saturated). One suitable amine-terminatedchain-extending agent is Ethacure 300™ (dimethylthiotoluenediamine or amixture of 2,6-diamino-3,5-dimethylthiotoluene and2,4-diamino-3,5-dimethylthiotoluene.) The amine curing agents used aschain extenders normally have a cyclic structure and a low molecularweight (250 or less).

When a hydroxyl-terminated curing agent is used, the resultingpolyurethane composition contains urethane linkages. On the other hand,when an amine-terminated curing agent is used, any excess isocyanategroups will react with the amine groups in the curing agent. Theresulting polyurethane composition contains urethane and urea linkagesand may be referred to as a polyurethane/urea hybrid.

Flex Modulus of Core Structure

As discussed above, the core of the golf ball of this inventionpreferably has a dual-layered structure comprising an inner core andouter core layer. Referring to FIG. 1, one version of a dual-layeredcore structure that can be made in accordance with this invention isgenerally indicated at (10). The dual-core subassembly (10) includes anon-foamed inner core (center) (12) and a surrounding foamed outer corelayer (14). The dual-core is used to construct a golf ball as shown inFIG. 2. Here, the golf ball (16) contains a dual-layered core (18)having a center (18 a) and outer core layer (18 b) surrounded by asingle-layered cover (19). In another version, referring to FIG. 3, thegolf ball (20) contains a dual-core (22) having a center (22 a) andouter core layer (22 b). The dual-core (22) is surrounded by amulti-layered cover (26) having an inner cover layer (26 a) and outercover layer (26 b).

Golf balls made in accordance with this invention can be of any size,although the USGA requires that golf balls used in competition have adiameter of at least 1.68 inches. For play outside of USGA rules, thegolf balls can be of a smaller size. Normally, golf balls aremanufactured in accordance with USGA requirements and have a diameter inthe range of about 1.68 to about 1.80 inches. As discussed furtherbelow, the golf ball contains a cover that may be multi-layered and alsomay contain intermediate (casing) layers, so the thickness levels ofthese layers also must be considered. In general, the dual-corestructure has an overall diameter within a range having a lower limit ofabout 1.00 or 1.20 or 1.30 or 1.40 inches and an upper limit of about1.55 or 1.58 or 1.60 or 1.63 or 1.65 inches. In one embodiment, thediameter of the core subassembly is in the range of about 1.20 to about1.60 inches. In another embodiment, the core subassembly has a diameterin the range of about 1.30 to about 1.58 inches, and in yet anotherversion, the core diameter is about 1.40 to about 1.55 inches.

Referring back to FIG. 1, the non-foamed inner core (12) can be of aconventional size and generally has a diameter within a range of about0.75 to about 1.50 inches. More particularly, the inner core (12)preferably has a diameter size with a lower limit of about 0.75 or 0.78or 0.80 or 0.92 or 1.00 inches and an upper limit of about 1.10 or 1.18or 1.30 or 1.40 or 1.44 or 1.50 inches. In one preferred version, thediameter of the non-foamed inner core (12) is in the range of about 0.75to about 1.25 inches, more preferably about 0.80 to about 1.10 inches.Meanwhile, the foamed outer core layer (14) has a relatively smallvolume and is a relatively thin layer. The outer core generally has athickness within a range of about 0.010 to about 0.250 inches andpreferably has a lower limit of 0.010 or 0.020 or 0.025 or 0.030 inchesand an upper limit of 0.070 or 0.080 or 0.100 or 0.200 inches. In onepreferred version, the foam outer core layer has a thickness in therange of about 0.040 to about 0.170 inches, more preferably about 0.060to about 0.150 inches.

In one preferred version of the dual-layered core construction, theinner core (center) is made from a relatively high modulus non-foamedcomposition, and the outer core layer is preferably made from arelatively low modulus foamed composition. By the term, “modulus” asused herein, it is meant flexural modulus which is the ratio of stressto strain within the elastic limit (when measured in the flexural mode)and is similar to tensile modulus. This property is used to indicate thebending stiffness of a material. The flexural modulus, which is amodulus of elasticity, is determined by calculating the slope of thelinear portion of the stress-strain curve during the bending test. Theformula used to calculate the flexural modulus from the recorded load(F) and deflection (D) is:

$E_{B} = {\frac{3}{4}\frac{{FL}^{3}}{{bd}^{3}D}}$

wherein,

L=span of specimen between supports (m);

b=width (m); and

d=thickness (m)

If the slope of the stress-strain curve is relatively steep, thematerial has a relatively high flexural modulus meaning the materialresists deformation. If the slope is relatively flat, the material has arelatively low flexural modulus meaning the material is more easilydeformed. Flexural modulus can be determined in accordance with ASTMD790 standard among other testing procedures.

The relatively low modulus foam compositions used to make the outer corepreferably have a modulus and material hardness less than the relativelyhigh modulus non-foamed compositions used to make the inner core.Preferably, the low modulus foam compositions have a lower limit of 100or 300 or 500 or 700 or 1,000 or 2,000 or 3,200 or 4,000 or 4,800 or5,100 psi and an upper limit of 6,000 or 6,400 or 7,000 or 7,800 or8,100 or 8,800 or 9,200 or 10,000 psi. On the other hand, the highmodulus non-foamed compositions (for example, polybutadiene rubber)preferably have a modulus within the range having a lower limit of 5,000or 6,000 or 8,500 or 10,000 or 15,200 or 18,000 or 20,000 or 24,200 or28,400 or 30,000 psi and an upper limit of 35,000 or 38,000 or 40,000 or42,000 or 44,600 or 45,000 or 48,000 or 50,000 or 52,000 or 54,200 or56,000 or 58,000 or 60,000. In a preferred embodiment, the modulus ofthe high modulus rubber composition is at least 10% greater, and morepreferably at least 20% greater than the modulus of the low modulusfoamed composition.

Hardness of Core Structure

The hardness of the core subassembly (inner core and outer core layer)also is an important property. In general, cores with relatively highhardness values have higher compression and tend to have good durabilityand resiliency. However, some high compression balls are stiff and thismay have a detrimental effect on feel, shot control, and ball placement.Thus, the optimum balance of hardness in the core subassembly needs tobe attained. As discussed above, the inner core is preferably formedfrom a non-foamed thermoplastic or thermoset composition such aspolybutadiene rubber. And, the outer core layer is formed preferablyfrom a foamed thermoplastic composition such as polyurethane.Dual-layered core structures containing layers with various thicknessand volume levels may be made in accordance with this invention.

In one preferred golf ball, the inner core (center) has a “positive”hardness gradient (that is, the outer surface of the inner core isharder than its geometric center); and the outer core layer has a“positive” hardness gradient (that is, the outer surface of the outercore layer is harder than the inner surface of the outer core layer.) Insuch cases where both the inner core and outer core layer each has a“positive” hardness gradient, the outer surface hardness of the outercore layer is preferably greater than the hardness of the geometriccenter of the inner core. In one preferred version, the positivehardness gradient of the inner core is in the range of about 2 to about40 Shore C units and even more preferably about 10 to about 25 Shore Cunits; while the positive hardness gradient of the outer core is in therange of about 2 to about 20 Shore C and even more preferably about 3 toabout 10 Shore C.

In an alternative version, the inner core may have a positive hardnessgradient; and the outer core layer may have a “zero” hardness gradient(that is, the hardness values of the outer surface of the outer corelayer and the inner surface of the outer core layer are substantiallythe same) or a “negative” hardness gradient (that is, the outer surfaceof the outer core layer is softer than the inner surface of the outercore layer.) For example, in one version, the inner core has a positivehardness gradient; and the outer core layer has a negative hardnessgradient in the range of about 2 to about 25 Shore C. In a secondalternative version, the inner core may have a zero or negative hardnessgradient; and the outer core layer may have a positive hardnessgradient. Still yet, in another embodiment, both the inner core andouter core layers have zero or negative hardness gradients.

In general, hardness gradients are further described in Bulpett et al.,U.S. Pat. Nos. 7,537,529 and 7,410,429, the disclosures of which arehereby incorporated by reference. Methods for measuring the hardness ofthe inner core and outer core layers along with other layers in the golfball and determining the hardness gradients of the various layers aredescribed in further detail below. The core layers have positive,negative, or zero hardness gradients defined by hardness measurementsmade at the outer surface of the inner core (or outer surface of theouter core layer) and radially inward towards the center of the innercore (or inner surface of the outer core layer). These measurements aremade typically at 2-mm increments as described in the test methodsbelow. In general, the hardness gradient is determined by subtractingthe hardness value at the innermost portion of the component beingmeasured (for example, the center of the inner core or inner surface ofthe outer core layer) from the hardness value at the outer surface ofthe component being measured (for example, the outer surface of theinner core or outer surface of the outer core layer).

Positive Hardness Gradient.

For example, if the hardness value of the outer surface of the innercore is greater than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface harder than its geometriccenter), the hardness gradient will be deemed “positive” (a largernumber minus a smaller number equals a positive number.) For example, ifthe outer surface of the inner core has a hardness of 67 Shore C and thegeometric center of the inner core has a hardness of 60 Shore C, thenthe inner core has a positive hardness gradient of 7. Likewise, if theouter surface of the outer core layer has a greater hardness value thanthe inner surface of the outer core layer, the given outer core layerwill be considered to have a positive hardness gradient.

Negative Hardness Gradient.

On the other hand, if the hardness value of the outer surface of theinner core is less than the hardness value of the inner core's geometriccenter (that is, the inner core has a surface softer than its geometriccenter), the hardness gradient will be deemed “negative.” For example,if the outer surface of the inner core has a hardness of 68 Shore C andthe geometric center of the inner core has a hardness of 70 Shore C,then the inner core has a negative hardness gradient of 2. Likewise, ifthe outer surface of the outer core layer has a lesser hardness valuethan the inner surface of the outer core layer, the given outer corelayer will be considered to have a negative hardness gradient.

Zero Hardness Gradient.

In another example, if the hardness value of the outer surface of theinner core is substantially the same as the hardness value of the innercore's geometric center (that is, the surface of the inner core hasabout the same hardness as the geometric center), the hardness gradientwill be deemed “zero.” For example, if the outer surface of the innercore and the geometric center of the inner core each has a hardness of65 Shore C, then the inner core has a zero hardness gradient. Likewise,if the outer surface of the outer core layer has a hardness valueapproximately the same as the inner surface of the outer core layer, theouter core layer will be considered to have a zero hardness gradient.

More particularly, the term, “positive hardness gradient” as used hereinmeans a hardness gradient of positive 3 Shore C or greater, preferably 7Shore C or greater, more preferably 10 Shore C, and even more preferably20 Shore C or greater. The term, “zero hardness gradient” as used hereinmeans a hardness gradient of less than 3 Shore C, preferably less than 1Shore C and may have a value of zero or negative 1 to negative 10 ShoreC. The term, “negative hardness gradient” as used herein means ahardness value of less than zero, for example, negative 3, negative 5,negative 7, negative 10, negative 15, or negative 20 or negative 25. Theterms, “zero hardness gradient” and “negative hardness gradient” may beused herein interchangeably to refer to hardness gradients of negative 1to negative 10.

The inner core preferably has a geometric center hardness(H_(inner core center)) of about 20 Shore D or greater. For example, the(H_(inner core center)) may be in the range of about 20 to about 80Shore D and more particularly within a range having a lower limit ofabout 20 or 22 or 26 or 30 or 34 or 36 or 38 or 42 or 48 or 50 or 52Shore D and an upper limit of about 54 or 56 or 58 or 60 or 62 or 64 or68 or 70 or 74 or 76 or 78 or 80 Shore D. In another example, the centerhardness of the inner core (H_(inner core center)), as measured in ShoreC units, is preferably about 30 Shore C or greater; for example, theH_(inner core center) may have a lower limit of about 30 or 34 or 37 or40 or 44 Shore C and an upper limit of about 46 or 48 or 50 or 51 or 53or 55 or 58 or 61 or 62 or 65 or 68 or 71 or 74 or 76 or 78 or 79 or 80or 84 or 90 or 95 Shore C.

Concerning the outer surface hardness of the inner core(H_(inner core surface)), this hardness is preferably about 20 Shore Dor greater; for example, the H_(inner core surface) may fall within arange having a lower limit of about 20 or 25 or 28 or 30 or 32 or 34 or36 or 40 or 42 or 48 or 50 and an upper limit of about 54 or 55 or 58 or60 or 63 or 65 or 68 or 70 or 74 or 78 or 80 or 82 or 85 Shore D. In oneversion, the outer surface hardness of the inner core(H_(inner core surface)), as measured in Shore C units, has a lowerlimit of about 30 or 32 or 35 or 38 or 40 or 42 Shore C and an upperlimit of about 45 or 48 or 50 or 53 or 56 or 58 or 60 or 62 or 65 or 68or 70 or 74 or 78 or 80 or 86 or 90 or 95 Shore C. In one version, thegeometric center hardness (H_(inner core center)) is in the range ofabout 30 Shore C to about 95 Shore C; and the outer surface hardness ofthe inner core (H_(inner core surface)) is in the range of about 30Shore C to about 95 Shore C.

On the other hand, the outer core layer preferably has an outer surfacehardness (H_(outer surface of OC)) of about 5 Shore D or greater, andmore preferably within a range having a lower limit of about 5 or 10 or12 or 15 or 18 or 20 or 24 or 30 and an upper limit of about 32 or 34 or35 or 38 or 40 or 42 or 45 or 50 or 52 or 58 or 60 Shore D. The outersurface hardness of the outer core layer (H_(outer surface of OC)), asmeasured in Shore C units, preferably has a lower limit of about 13 or15 or 18 or 20 or 24 or 28 or 30 or 33 and an upper limit of about 35 or37 or 38 or 40 or 42 or 44 or 48 or 50 or 52 or 55 or 60 Shore C.

And, the inner surface of the outer core layer (H_(inner surface of OC))or midpoint hardness of the outer core layer (H_(midpoint of OC)),preferably has a hardness of about 4 Shore D or greater, and morepreferably within a range having a lower limit of about 4 or 6 or 8 or10 or 12 or 14 or 18 or 20 or 24 and an upper limit of about 30 or 34 or38 or 40 or 44 or 46 or 52 Shore D. The inner surface hardness(H_(inner surface of OC)) or midpoint hardness (H_(midpoint of OC)) ofthe outer core layer, as measured in Shore C units, preferably has alower limit of about 10 or 12 or 14 or 17 or 20 or 22 or 24 Shore C, andan upper limit of about 28 or 30 or 35 or 38 or 40 or 42 or 45 or 48 or52 or 55 Shore C.

In one embodiment, the outer surface hardness of the outer core layer(H_(outer surface of OC)), is less than the outer surface hardness(H_(inner core surface)) or midpoint hardness (H_(midpoint of OC)), ofthe outer core by at least 3 Shore C units and more preferably by atleast 5 Shore C.

In a second embodiment, the outer surface hardness of the outer corelayer (H_(outer surface of OC)), is greater than the outer surfacehardness (H_(inner core surface)) or midpoint hardness(H_(midpoint of OC)), of the outer core by at least 3 Shore C units andmore preferably by at least 5 Shore C.

The core structure also has a hardness gradient across the entire coreassembly. In one embodiment, the (H_(inner core center)) is in the rangeof about 30 to about 95 Shore C, preferably about 45 to about 75 ShoreC; and the (H_(outer surface of OC)) is in the range of about 13 toabout 60 Shore C, preferably about 20 to about 50 Shore C to provide anegative hardness gradient across the core assembly.

In another embodiment, the H_(inner core center) is in the range ofabout 35 to about 55 Shore C and the H_(outer surface of OC) is in therange of about 40 to about 60 Shore C to provide a positive hardnessgradient across the core assembly. The gradient will vary based onseveral factors including, but not limited to, the dimensions of theinner core and outer core layers.

The outer surface hardness of the foam outer core layer(H_(outer surface of OC)), as measured in Shore A units, preferably hasa lower limit of about 30 or 35 or 38 or 40 or 44 or 48 and an upperlimit of about 55 or 57 or 60 or 62 or 64 or 68 or 70 or 72 or 75 or 80or 85 or 88 or 90 or 95 or 100. The inner surface hardness(H_(inner surface of OC)) or midpoint hardness (H_(midpoint of OC)) ofthe foam outer core layer, as measured in Shore A units, preferably hasa lower limit of about 25 or 28 or 30 or 34 or 37 or 40 or 22 or 24 or30 or 34 or 40 Shore A, and an upper limit of about 50 or 52 or 55 or 58or 60 or 62 or 65 or 70 or 72 or 76 or 80 or 88 or 91 or 95 Shore A.

Specific Gravity (Density) of Core Structure

As discussed above, the core of the golf ball of this inventionpreferably has a dual-layered construction comprising inner and outercore layers. The USGA has established a maximum weight of 45.93 g (1.62ounces) for golf balls. For play outside of USGA rules, the golf ballscan be heavier. Since the golf ball contains a cover and also maycontain intermediate (casing) layers, the weight of these layers alsomust be considered. In one preferred embodiment, the weight of thedual-layered core is in the range of about 28 to about 42 grams.

The specific gravity of inner core layer (SG_(inner)) is preferablygreater than the specific gravity of the outer core layer (SG_(outer)).The specific gravity (density) of the respective core layers is animportant property, because they affect the Moment of Inertia (MOI) ofthe ball. In one preferred embodiment, the inner core layer has arelatively high specific gravity (“SG_(inner)”). For example, the innercore layer may have a specific gravity within a range having a lowerlimit of about 0.60 or 0.64 or 0.66 or 0.70 or 0.72 or 0.75 or 0.78 or0.80 or 0.82 or 0.85 or 0.88 or 0.90 g/cc and an upper limit of about or0.95 or 1.00 or 1.05 or 1.10 or 1.14 or 1.20 or 1.25 or 1.30 or 1.36 or1.40 or 1.42 or 1.48 or 1.50 or 1.60 or 1.66 or 1.70 1.75 or 2.008/cc.In a particularly preferred version, the inner core has a specificgravity of about 1.05 g/cc. Meanwhile, the foamed outer core layerpreferably has a relatively low specific gravity (SG_(outer)). Forexample, the outer core layer may have a specific gravity within a rangehaving a lower limit of about 0.20 or 0.34 or 0.28 or 0.30 or 0.34 or0.35 or 0.40 or 0.42 or 0.44 or 0.50 or 0.53 or 0.57 or 0.60 or 0.62 or0.65 or 0.70 or 0.75 or 0.77 or 0.80 g/cc and an upper limit of about0.82 or 0.85 or 0.88 or 0.90 or 0.95 or 1.00 or 1.10 or 1.15 or 1.18 or1.25 g/cc or 1.32 or 1.35 or 1.38 or 1.42 or 1.45 or 1.48 or 1.50 or1.52 or 1.56. In a particularly preferred version, the outer core has aspecific gravity of about 0.50 g/cc.

Thus, the specific gravity of the inner core layer (SG_(inner)) ispreferably greater than the specific gravity of the foamed outer corelayer (SG_(outer)). When comparing the specific gravities of the outerand inner core layers, it is generally meant by the term, “specificgravity of the outer core layer” (“SG_(outer)”), the specific gravity ofthe outer core layer as measured at any point in the outer core layer.Likewise, by the term, “specific gravity of the inner core layer”(“SG_(inner)”), it is generally meant the specific gravity of the innercore layer as measured at any point in the inner core layer. However, itis recognized the specific gravity of the inner and outer core layersmay vary at different particular points within the respective corelayers. Thus, there may be specific gravity gradients within the innerand outer core layers. For example, the midpoint region of the foamedcomposition comprising the outer core may have a density in the range ofabout 0.25 to about 0.75 g/cc; while the outer skin of the foamcomposition (outer surface of the outer core) may have a density in therange of about 0.75 to about 1.35 g/cc. These specific gravity gradientswithin the core layers are discussed further below.

There are several different ways of creating a specific gravity gradientwithin the core layers, particularly the foamed outer core layer. Thesemethods include, for example, the following: 1) The foam composition canbe treated so that it includes a fully-foamed region and a partially orcompletely-collapsed foam outer region. The density of the collapsedfoam region is greater than the density of the fully-foamed region. Heatcan be used to partially-collapse the foamed outer region and make itdenser. This method is described in further detail below. 2) Foamshaving an open cell morphology, where the cells walls are incomplete orcontain small holes can be prepared. These foams can be soaked in one ormore reactive liquids so the liquid permeates a portion of the foam andreacts to form a region of greater density. This region can be curedresulting in a layer having a density gradient. 3) Secondary blowingagents that can be activated by heat or over-molding of additionallayers also can be used to create a density gradient.

In one embodiment, the method for making the core assembly (non-foamedinner core and surrounding foamed outer core layer) comprises thefollowing steps. First, a non-foam composition is molded into an innercore structure. Secondly, a foam composition is molded into an outercore structure. Then, the foamed outer core structure is thermally orchemically-treated so as to at least partially-collapse the foam in theouter region. In some instances, the foam in the outer region iscompletely collapsed by this treatment.

Referring to FIG. 5, in one preferred embodiment, a core assembly (33)comprising an inner core (34) made from a non-foamed composition and anouter core (36) made from a foamed composition, as described above, isshown. The foamed outer core (36) includes a midpoint region (38) andsurrounding outer surface region (40) and outer surface (42). When theouter core layer (36) is first made, the midpoint region (38) andsurrounding outer region (40) are foamed. But, the outer surface (42) ofthe outer core is generally a non-foamed, and relatively thin and denselayer. This surface may be referred to as the “skin” of the foamedcomposition. In one embodiment, the thickness of the outer skin (42) isin the range of about 0.001 inches (1 mil) to about 0.050 inches (50mils) and preferably in the range of about 0.010 to about 0.030 inches.In one particular example, the thickness of the outer skin (42) can beless than about 0.025 inches and even less than 0.015 inches.

In a subsequent step, as described in further detail below, the foamedouter core layer (36) is thermally or chemically-treated. For example,in one preferred embodiment, an inner cover layer is over-molded theouter core structure. In this process, the heat used in the moldingcycle activates/decomposes the foamed outer region (40) of the outercore (36). This over-molding step causes the foamed outer region (40) ofthe outer core (36) to at least partially collapse. The foamed outerregion (40) becomes at least partially non-foamed as the foam collapses.The outer region (40) becomes more dense (that is, less foamed). In someinstances, the foamed outer region (40) collapses completely and becomescompletely non-foamed.

Referring to FIG. 6, the outer core (36) is shown with a foamed midpointregion (38) and partially-collapsed outer region (40) and outer surface(skin) (42). An inner cover (46), which is formed by an over-moldingprocess, surrounds the outer core (36). In some instances, the foam inthe outer region (40) is completely collapsed by this treatment.Meanwhile, the foamed state of the midpoint region (38) is maintained.The foamed geometric center, partially-collapsed outer region, and outerskin of the outer core layer have different morphologies. For example,there is generally lower volume of foam cells in the partially-collapsedouter region. An inner cover layer (46), which is formed by theover-molding process, surrounds the outer core (36). An outer coverlayer (not shown in FIG. 6) can be molded over the inner cover layer(46) using techniques as described further below.

The inner cover layer (46) may be molded over the foamed outer core (36)using a variety of molding methods that involve subjecting the core (36)to heat and pressure. For example, the inner cover composition (46)(preferably a thermoplastic composition) may be injection-molded orcompression-molded to produce half-shells. These smooth-surfaced ortextured hemispherical shells are then placed around the foamed,spherical outer core in a compression mold. Under sufficient heating andpressure, the shells fuse together to form an inner cover layer thatencapsulates the foamed outer core. More particularly, the twohalf-shells made from a thermoplastic composition may be prepared, andthen they are joined together in a mold to encase the previously moldedouter core. The hemispherical shells and core assembly are placed in amold between first and second mold members which are subsequentlypressed together under sufficient heat and pressure. This moldingprocess forms the inner cover layer. In another method, a retractablepin injection-molding method may be used to form the inner cover.

This heat/pressure treatment creates a non-foamed outer region (40)having different properties than the foamed midpoint region (38) of theouter core layer (36). For example, in one preferred embodiment, thehardness of the outer region (40) is greater than the hardness of themidpoint region (38) to create a positive hardness gradient across theouter core layer (36). These hardness gradients are discussed in furtherdetail below. The specific gravity (or density) of the outer region (40)also may be greater than the specific gravity of the midpoint region(38). That is, there can be specific gravity gradients within the foamedouter core layer.

For example, the foamed outer core layer (36) may have an outer surfacespecific gravity (SG_(outer core surface)) and a midpoint specificgravity (SG_(outer core midpoint)), wherein the SG_(outer core surface)is greater than the SG_(outer core midpoint). For example, the midpointspecific gravity can be within a range having a lower limit of about0.20 or 0.24 or 0.28 or 0.30 or 0.34 or 0.35 or 0.40 or 0.42 or 0.44 or0.50 or 0.53 or 0.57 or 0.60 or 0.62 or 0.65 or 0.70 or 0.75 or 0.77 or0.80 and a higher limit of about 0.82 or 0.85 or 0.88 or 0.90 or 0.95 or1.00 or 1.10 or 1.15 or 1.18 or 1.25 g/cc or 1.32 or 1.35 or 1.38 or1.42 or 1.45 or 1.48 or 1.50 or 1.52 or 1.57 or 1.60. The foamed outercore also has a specific gravity in the outer region(SG_(outer core outer region)) and outer surface(SG_(outer core surface)) as discussed above. For example, the specificgravity of the outer region and/or outer surface can be within a rangehaving a lower limit of 0.21 or 0.35 or 0.29 or 0.31 or 0.35 or 0.36 or0.41 or 0.43 or 0.45 or 0.51 or 0.54 or 0.58 or 0.61 or 0.63 or 0.66 or0.71 or 0.76 or 0.78 or 0.81 g/cc and a higher limit of about 0.83 or0.86 or 0.89 or 0.91 or 0.96 or 1.01 or 1.11 or 1.16 or 1.19 or 1.26g/cc or 1.33 or 1.36 or 1.39 or 1.43 or 1.46 or 1.49 or 1.51 or 1.53 or1.58 or 1.61. In one preferred embodiment, the SG_(outer core surface)is greater than the SG_(outer core outer region) and theSG_(outer core outer region) is greater than theSG_(outer core midpoint). Thus, in one version, theSG_(outer core surface)>SG_(outer core outer region)>SG_(outer core midpoint)by at least 0.01, more preferably by at least 0.05, and most preferablyby at least 0.1. In another preferred version, theSG_(outer core surface) is greater than or equal toSG_(outer core outer region) and is greater than theSG_(outer core midpoint) by at least 0.01, more preferably 0.05, andmost preferably 0.1.

In an alternative method, a chemical-treatment may also be used to forman outer region of greater density in the outer core layer (36). Forexample, the foamed sphere may be exposed to a solvent that partiallydissolves or softens the outer portion of the sphere in order to causeit to collapse slightly. It is also possible to treat the foamed spherewith a reactive mixture such as polyurethane, polyurea, epoxy, or otherreactive polymer system. The liquid, non-reacted mixture can fill thevoids of the outer region (40) of the foamed sphere and react to form asolid material. In this manner, the density of the outer region (40) ofthe foamed sphere can be increased.

In general, the specific gravities of the respective pieces of an objectaffect the Moment of Inertia (MOI) of the object. The Moment of Inertiaof a ball (or other object) about a given axis generally refers to howdifficult it is to change the ball's angular motion about that axis. Ifthe ball's mass is concentrated towards the center, less force isrequired to change its rotational rate, and the ball has a relativelylow Moment of Inertia. In such balls, the center piece (that is, theinner core) has a higher specific gravity than the outer piece (that is,the outer core layer). In such balls, most of the mass is located closeto the ball's axis of rotation and less force is needed to generatespin. Thus, the ball has a generally high spin rate as the ball leavesthe club's face after making impact. Because of the high spin rate,amateur golfers may have a difficult time controlling the ball andhitting it in a relatively straight line. Such high-spin balls tend tohave a side-spin so that when a golfer hook or slices the ball, it maydrift off-course.

Conversely, if the ball's mass is concentrated towards the outersurface, more force is required to change its rotational rate, and theball has a relatively high Moment of Inertia. In such balls, the centerpiece (that is, the inner core) has a lower specific gravity than theouter piece (that is, the outer core layer). That is, in such balls,most of the mass is located away from the ball's axis of rotation andmore force is needed to generate spin. Thus, the ball has a generallylow spin rate as the ball leaves the club's face after making impact.Because of the low spin rate, amateur golfers may have an easier timecontrolling the ball and hitting it in a relatively straight line. Theball tends to travel a greater distance which is particularly importantfor driver shots off the tee.

As described in Sullivan, U.S. Pat. No. 6,494,795 and Ladd et al., U.S.Pat. No. 7,651,415, the formula for the Moment of Inertia for a spherethrough any diameter is given in the CRC Standard Mathematical Tables,24th Edition, 1976 at 20 (hereinafter CRC reference). The term,“specific gravity” as used herein, has its ordinary and customarymeaning, that is, the ratio of the density of a substance to the densityof water at 4° C., and the density of water at this temperature is 1g/cm³.

The golf balls of this invention having the above-described coreconstructions show both good resiliency and spin control. In the ballsof this invention, the specific gravity of the inner core layer(SG_(inner)) is preferably greater than the specific gravity of theouter core layer (SG_(outer)). The specific gravity of the inner corelayer (SG_(inner)) also is preferably greater than the specific gravityof the intermediate (casing) layers (if such layers are present); andthe inner and outer cover layers. Still, the overall density of the coreis generally balanced. As discussed above, the non-foamed compositionused to make the inner core has a relatively high specific gravity.However, the foamed composition used to make the surrounding outer corelayer is slightly positioned away from the center of the ball. Thus, theball does not have a relatively high or low moment of inertia. Rather,the ball can be described as having a relative “medium moment ofinertia.”

The foam cores and resulting balls also have relatively high resiliencyso the ball will reach a relatively high velocity when struck by a golfclub and travel a long distance. In particular, the inner foam cores ofthis invention preferably have a Coefficient of Restitution (COR) ofabout 0.300 or greater; more preferably about 0.400 or greater, and evenmore preferably about 0.450 or greater. The resulting balls containingthe dual-layered core constructions of this invention and cover of atleast one layer preferably have a COR of about 0.700 or greater, morepreferably about 0.730 or greater; and even more preferably about 0.750to 0.810 or greater. Also, the foam cores preferably have a Soft CenterDeflection Index (“SCDI”) compression, as described in the Test Methodsbelow, in the range of about 50 to about 190, and more preferably in therange of about 60 to about 170.

Cover Structure

The golf ball sub-assemblies of this invention may be enclosed with oneor more cover layers. The golf ball subassembly may comprise themulti-layered core structure as discussed above. In other versions, thegolf ball subassembly includes the core structure and one or more casing(mantle) layers disposed about the core. In one version, the golf ballincludes a multi-layered cover comprising inner and outer cover layers.The inner cover layer is preferably formed from a composition comprisingan ionomer or a blend of two or more ionomers that helps impart hardnessto the ball. In a particular embodiment, the inner cover layer is formedfrom a composition comprising a high acid ionomer. A particularlysuitable high acid ionomer is Surlyn 8150® (DuPont). Surlyn 8150® is acopolymer of ethylene and methacrylic acid, having an acid content of 19wt %, which is 45% neutralized with sodium. In another particularembodiment, the inner cover layer is formed from a compositioncomprising a high acid ionomer and a maleic anhydride-graftednon-ionomeric polymer. A particularly suitable maleic anhydride-graftedpolymer is Fusabond 525D® (DuPont). Fusabond 525D® is a maleicanhydride-grafted, metallocene-catalyzed ethylene-butene copolymerhaving about 0.9 wt % maleic anhydride grafted onto the copolymer. Aparticularly preferred blend of high acid ionomer and maleicanhydride-grafted polymer is an 84 wt %/16 wt % blend of Surlyn 8150®and Fusabond 525D®. Blends of high acid ionomers with maleicanhydride-grafted polymers are further disclosed, for example, in U.S.Pat. Nos. 6,992,135 and 6,677,401, the entire disclosures of which arehereby incorporated herein by reference.

The inner cover layer also may be formed from a composition comprising a50/45/5 blend of Surlyn® 8940/Surlyn® 9650/Nucrel® 960, and, in aparticularly preferred embodiment, the composition has a materialhardness of from 80 to 85 Shore C. In yet another version, the innercover layer is formed from a composition comprising a 50/25/25 blend ofSurlyn® 8940/Surlyn® 9650/Surlyn® 9910, preferably having a materialhardness of about 90 Shore C. The inner cover layer also may be formedfrom a composition comprising a 50/50 blend of Surlyn® 8940/Surlyn®9650, preferably having a material hardness of about 86 Shore C. Acomposition comprising a 50/50 blend of Surlyn® 8940 and Surlyn® 7940also may be used. Surlyn® 8940 is an E/MAA copolymer in which the MAAacid groups have been partially neutralized with sodium ions. Surlyn®9650 and Surlyn® 9910 are two different grades of E/MAA copolymer inwhich the MAA acid groups have been partially neutralized with zincions. Nucrel® 960 is an E/MAA copolymer resin nominally made with 15 wt% methacrylic acid.

A wide variety of materials may be used for forming the outer coverincluding, for example, polyurethanes; polyureas; copolymers, blends andhybrids of polyurethane and polyurea; olefin-based copolymer ionomerresins (for example, Surlyn® ionomer resins and DuPont HPF® 1000 andHPF® 2000, commercially available from DuPont; Iotek® ionomers,commercially available from ExxonMobil Chemical Company; Amplify® 10ionomers of ethylene acrylic acid copolymers, commercially availablefrom The Dow Chemical Company; and Clarix® ionomer resins, commerciallyavailable from A. Schulman Inc.); polyethylene, including, for example,low density polyethylene, linear low density polyethylene, and highdensity polyethylene; polypropylene; rubber-toughened olefin polymers;acid copolymers, for example, poly(meth)acrylic acid, which do notbecome part of an ionomeric copolymer; plastomers; flexomers;styrene/butadiene/styrene block copolymers;styrene/ethylene-butylene/styrene block copolymers; dynamicallyvulcanized elastomers; copolymers of ethylene and vinyl acetates;copolymers of ethylene and methyl acrylates; polyvinyl chloride resins;polyamides, poly(amide-ester) elastomers, and graft copolymers ofionomer and polyamide including, for example, Pebax® thermoplasticpolyether block amides, commercially available from Arkema Inc;cross-linked trans-polyisoprene and blends thereof; polyester-basedthermoplastic elastomers, such as Hytrel®, commercially available fromDuPont or RiteFlex®, commercially available from Ticona EngineeringPolymers; polyurethane-based thermoplastic elastomers, such asElastollan®, commercially available from BASF; synthetic or naturalvulcanized rubber; and combinations thereof. Castable polyurethanes,polyureas, and hybrids of polyurethanes-polyureas are particularlydesirable because these materials can be used to make a golf ball havinghigh resiliency and a soft feel. By the term, “hybrids of polyurethaneand polyurea,” it is meant to include copolymers and blends thereof.

Polyurethanes, polyureas, and blends, copolymers, and hybrids ofpolyurethane/polyurea are also particularly suitable for forming coverlayers. When used as cover layer materials, polyurethanes and polyureascan be thermoset or thermoplastic. Thermoset materials can be formedinto golf ball layers by conventional casting or reaction injectionmolding techniques. Thermoplastic materials can be formed into golf balllayers by conventional compression or injection molding techniques.

The inner cover layer preferably has a material hardness within a rangehaving a lower limit of 70 or 75 or 80 or 82 Shore C and an upper limitof 85 or 86 or 90 or 92 Shore C. The thickness of the inner cover layeris preferably within a range having a lower limit of 0.010 or 0.015 or0.020 or 0.030 inches and an upper limit of 0.035 or 0.045 or 0.080 or0.120 inches. The outer cover layer preferably has a material hardnessof 85 Shore C or less. The thickness of the outer cover layer ispreferably within a range having a lower limit of 0.010 or 0.015 or0.025 inches and an upper limit of 0.035 or 0.040 or 0.055 or 0.080inches. Methods for measuring hardness of the layers in the golf ballare described in further detail below.

As discussed above, the core structure of this invention may be enclosedwith one or more cover layers. In one embodiment, a multi-layered covercomprising inner and outer cover layers is formed, where the inner coverlayer has a thickness of about 0.01 inches to about 0.06 inches, morepreferably about 0.015 inches to about 0.040 inches, and most preferablyabout 0.02 inches to about 0.035 inches. In this version, the innercover layer is formed from a partially- or fully-neutralized ionomerhaving a Shore D hardness of greater than about 55, more preferablygreater than about 60, and most preferably greater than about 65. Theouter cover layer, in this embodiment, preferably has a thickness ofabout 0.015 inches to about 0.055 inches, more preferably about 0.02inches to about 0.04 inches, and most preferably about 0.025 inches toabout 0.035 inches, with a hardness of about Shore D 80 or less, morepreferably 70 or less, and most preferably about 60 or less. The innercover layer is harder than the outer cover layer in this version. Apreferred outer cover layer is a castable or reaction injection moldedpolyurethane, polyurea or copolymer, blend, or hybrid thereof having aShore D hardness of about 40 to about 50. In another multi-layer cover,dual-core embodiment, the outer cover and inner cover layer materialsand thickness are the same but, the hardness range is reversed, that is,the outer cover layer is harder than the inner cover layer. For thisharder outer cover/softer inner cover embodiment, the ionomer resinsdescribed above would preferably be used as outer cover material.

Golf Ball Construction

The solid cores for the golf balls of this invention may be made usingany suitable conventional technique such as, for example, compression orinjection molding. In some embodiments, the inner core is formed bycompression molding a slug of the uncured or lightly cured polybutadienerubber material into a substantially spherical structure. The outer corelayer, which surround the inner core, are formed by molding compositionsover the inner core. Compression or injection molding techniques may beused. Then, the intermediate (casing) and/or cover layers are applied.Prior to this step, the core structure may be surface-treated toincrease the adhesion between its outer surface and the next layer thatwill be applied over the core. Such surface-treatment may includemechanically or chemically-abrading the outer surface of the core. Forexample, the core may be subjected to corona-discharge,plasma-treatment, silane-dipping, or other treatment methods known tothose in the art.

The casing and cover layers are formed over the ball subassembly (corestructure) using a suitable technique such as, for example,compression-molding, flip-molding, injection-molding, retractable pininjection-molding, reaction injection-molding, liquid injection-molding,casting, spraying, powder-coating, vacuum-forming, flow-coating,dipping, spin-coating, and the like. Preferably, each cover layer isseparately formed over the ball subassembly. For example, an ethyleneacid copolymer ionomer composition may be injection-molded to producehalf-shells. Alternatively, the ionomer composition can be placed into acompression mold and molded under sufficient pressure, temperature, andtime to produce the hemispherical shells. The smooth-surfacedhemispherical shells are then placed around the ball subassembly in acompression mold. Under sufficient heating and pressure, the shells fusetogether to form an inner cover layer that surrounds the subassembly. Inanother method, the ionomer composition is injection-molded directlyonto the core using retractable pin injection molding. An outer coverlayer comprising a polyurethane or polyurea composition may be formed byusing a casting process.

For example, in one version of the casting process, a liquid mixture ofreactive polyurethane prepolymer and chain-extender (curing agent) ispoured into lower and upper mold cavities. Then, the golf ballsubassembly is lowered at a controlled speed into the reactive mixture.Ball suction cups can hold the ball subassembly in place via reducedpressure or partial vacuum. After sufficient gelling of the reactivemixture (typically about 4 to about 12 seconds), the vacuum is removedand the intermediate ball is released into the mold cavity. Then, theupper mold cavity is mated with the lower mold cavity under sufficientpressure and heat. An exothermic reaction occurs when the polyurethaneprepolymer and chain extender are mixed and this continues until thecover material encapsulates and solidifies around the ball subassembly.Finally, the molded balls are cooled in the mold and removed when themolded cover is hard enough so that it can be handled withoutdeformation.

In one such casting process, a polyurethane prepolymer and curing agentare mixed in a motorized mixer inside of a mixing head by meteringamounts of the curative and prepolymer through the feed lines. A moldhaving upper and lower hemispherical-shaped mold cavities and withinterior dimple patterns is used. Each mold cavity has an arcuate innersurface defining an inverted dimple pattern. The upper and lower moldcavities can be preheated and filled with the reactive polyurethane andcuring agent mixture. After the reactive mixture has resided in thelower mold cavities for a sufficient time period, typically about 40 toabout 100 seconds, the golf ball core/inner cover assembly can belowered at a controlled speed into the reacting mixture. Ball cups canhold the assemblies by applying reduced pressure (or partial vacuum).After sufficient gelling (typically about 4 to about 12 seconds), thevacuum can be removed and the assembly can be released. Then, the upperhalf-molds can be mated with the lower half-molds. An exothermicreaction occurs when the polyurethane prepolymer and curing agent aremixed and this continues until the material solidifies around thesubassembly. The molded balls can then be cooled in the mold and removedwhen the molded cover layer is hard enough to be handled withoutdeforming. This molding technique is described in the patent literatureincluding Hebert et al., U.S. Pat. No. 6,132,324, Wu, U.S. Pat. No.5,334,673, and Brown et al., U.S. Pat. No. 5,006,297, the disclosures ofwhich are hereby incorporated by reference.

As discussed above, the lower and upper mold cavities have interiordimple cavity details. When the mold cavities are mated together, theydefine an interior spherical cavity that forms the cover for the ball.The cover material encapsulates the inner ball subassembly to form aunitary, one-piece cover structure. Furthermore, the cover materialconforms to the interior geometry of the mold cavities to form a dimplepattern on the surface of the ball. The mold cavities may have anysuitable dimple arrangement such as, for example, icosahedral,octahedral, cube-octahedral, dipyramid, and the like. In addition, thedimples may be circular, oval, triangular, square, pentagonal,hexagonal, heptagonal, octagonal, and the like.

After the golf balls have been removed from the mold, they may besubjected to finishing steps such as flash-trimming, surface-treatment,marking, coating, and the like using techniques known in the art. Forexample, in traditional white-colored golf balls, the white-pigmentedcover may be surface-treated using a suitable method such as, forexample, corona, plasma, or ultraviolet (UV) light-treatment. Then,indicia such as trademarks, symbols, logos, letters, and the like may beprinted on the ball's cover using pad-printing, ink-jet printing,dye-sublimation, or other suitable printing methods. Clear surfacecoatings (for example, primer and top-coats), which may contain afluorescent whitening agent, are applied to the cover. The resultinggolf ball has a glossy and durable surface finish. In FIG. 4, a finishedgolf ball (30) having an outer cover with a dimpled surface (32) isshown.

In another finishing process, the golf balls are painted with one ormore paint coatings. For example, white primer paint may be appliedfirst to the surface of the ball and then a white top-coat of paint maybe applied over the primer. Of course, the golf ball may be painted withother colors, for example, red, blue, orange, and yellow. As notedabove, markings such as trademarks and logos may be applied to thepainted cover of the golf ball. Finally, a clear surface coating may beapplied to the cover to provide a shiny appearance and protect any logosand other markings printed on the ball.

Different core and ball constructions can be made per this invention asshown in FIGS. 1-6 discussed above. Such golf ball designs include, forexample, three-piece, four-piece, five-piece, and six-piece designs. Itshould be understood that the core constructions and golf balls shown inFIGS. 1-6 are for illustrative purposes only and are not meant to berestrictive. Other core constructions and golf balls can be made inaccordance with this invention.

Cores Having Three Layers

For example, multi-layered cores having an inner core, intermediate corelayer, and outer core layer, wherein the intermediate core layer isdisposed between the intermediate and outer core layers may be preparedin accordance with this invention. More particularly, as discussedabove, the inner core may be constructed from a non-foamed thermoset orthermoplastic material, preferably polybutadiene rubber as discussedabove. Meanwhile, the intermediate and outer core layers may be formedfrom foamed compositions, preferably foamed polyurethane as discussedabove. In another embodiment, the inner core layer is formed from anon-foamed thermoset or thermoplastic composition; the intermediate corelayer is formed from a foamed composition; and the outer core layer isformed from a non-foamed thermoset or thermoplastic composition. Thespecific gravity of the core layer(s) comprising the foam composition ispreferably less than the specific gravity of the core layer(s)comprising the non-foamed composition(s).

Where more than one foam layer is used in a single golf ball, therespective foamed chemical compositions may be the same or different,and the compositions may have the same or different hardness or specificgravity levels. For example, a golf ball may contain a three-layeredcore having a non-foamed polybutadiene rubber center; a polyurethanefoam intermediate core layer; and an outer core layer comprising afoamed highly-neutralized ionomer (HNP) composition.

Test Methods

Hardness.

The center hardness of a core is obtained according to the followingprocedure. The core is gently pressed into a hemispherical holder havingan internal diameter approximately slightly smaller than the diameter ofthe core, such that the core is held in place in the hemisphericalportion of the holder while concurrently leaving the geometric centralplane of the core exposed. The core is secured in the holder byfriction, such that it will not move during the cutting and grindingsteps, but the friction is not so excessive that distortion of thenatural shape of the core would result. The core is secured such thatthe parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut is made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight from the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within 0.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center markaccording to ASTM D-2240. Additional hardness measurements at anydistance from the center of the core can then be made by drawing a lineradially outward from the center mark, and measuring the hardness at anygiven distance along the line, typically in 2 mm increments from thecenter. The hardness at a particular distance from the center should bemeasured along at least two, preferably four, radial arms located 180°apart, or 90° apart, respectively, and then averaged. All hardnessmeasurements performed on a plane passing through the geometric centerare performed while the core is still in the holder and without havingdisturbed its orientation, such that the test surface is constantlyparallel to the bottom of the holder, and thus also parallel to theproperly aligned foot of the durometer.

The outer surface hardness of a golf ball layer is measured on theactual outer surface of the layer and is obtained from the average of anumber of measurements taken from opposing hemispheres, taking care toavoid making measurements on the parting line of the core or on surfacedefects, such as holes or protrusions. Hardness measurements are madepursuant to ASTM D-2240 “Indentation Hardness of Rubber and Plastic byMeans of a Durometer.” Because of the curved surface, care must be takento ensure that the golf ball or golf ball subassembly is centered underthe durometer indenter before a surface hardness reading is obtained. Acalibrated, digital durometer, capable of reading to 0.1 hardness unitsis used for the hardness measurements. The digital durometer must beattached to, and its foot made parallel to, the base of an automaticstand. The weight on the durometer and attack rate conforms to ASTMD-2240.

In certain embodiments, a point or plurality of points measured alongthe “positive” or “negative” gradients may be above or below a line fitthrough the gradient and its outermost and innermost hardness values. Inan alternative preferred embodiment, the hardest point along aparticular steep “positive” or “negative” gradient may be higher thanthe value at the innermost portion of the inner core (the geometriccenter) or outer core layer (the inner surface)—as long as the outermostpoint (i.e., the outer surface of the inner core) is greater than (for“positive”) or lower than (for “negative”) the innermost point (i.e.,the geometric center of the inner core or the inner surface of the outercore layer), such that the “positive” and “negative” gradients remainintact.

As discussed above, the direction of the hardness gradient of a golfball layer is defined by the difference in hardness measurements takenat the outer and inner surfaces of a particular layer. The centerhardness of an inner core and hardness of the outer surface of an innercore in a single-core ball or outer core layer are readily determinedaccording to the test procedures provided above. The outer surface ofthe inner core layer (or other optional intermediate core layers) in adual-core ball are also readily determined according to the proceduresgiven herein for measuring the outer surface hardness of a golf balllayer, if the measurement is made prior to surrounding the layer with anadditional core layer. Once an additional core layer surrounds a layerof interest, the hardness of the inner and outer surfaces of any inneror intermediate layers can be difficult to determine. Therefore, forpurposes of the present invention, when the hardness of the inner orouter surface of a core layer is needed after the inner layer has beensurrounded with another core layer, the test procedure described abovefor measuring a point located 1 mm from an interface is used. Likewise,the midpoint of a core layer is taken at a point equidistant from theinner surface and outer surface of the layer to be measured, mosttypically an outer core layer. It is recognized that when one or morecore layers surround a layer of interest, the exact midpoint may bedifficult to determine, therefore, for the purposes of the presentinvention, the measurement of “midpoint” hardness of a layer is takenwithin plus or minus 1 mm of the measured midpoint of the layer.

Also, it should be understood that there is a fundamental differencebetween “material hardness” and “hardness as measured directly on a golfball.” For purposes of the present invention, material hardness ismeasured according to ASTM D2240 and generally involves measuring thehardness of a flat “slab” or “button” formed of the material. Surfacehardness as measured directly on a golf ball (or other sphericalsurface) typically results in a different hardness value. The differencein “surface hardness” and “material hardness” values is due to severalfactors including, but not limited to, ball construction (that is, coretype, number of cores and/or cover layers, and the like); ball (orsphere) diameter; and the material composition of adjacent layers. Italso should be understood that the two measurement techniques are notlinearly related and, therefore, one hardness value cannot easily becorrelated to the other. Shore hardness (for example, Shore A, Shore Cor Shore D hardness) was measured according to the test method ASTMD-2240.

Compression.

As disclosed in Jeff Dalton's Compression by Any Other Name, Science andGolf IV, Proceedings of the World Scientific Congress of Golf (EricThain ed., Routledge, 2002) (“J. Dalton”), several different methods canbe used to measure compression, including Atti compression, Riehlecompression, load/deflection measurements at a variety of fixed loadsand offsets, and effective modulus. For purposes of the presentinvention, compression refers to Soft Center Deflection Index (“SCDI”).The SCDI is a program change for the Dynamic Compression Machine (“DCM”)that allows determination of the pounds required to deflect a core 10%of its diameter. The DCM is an apparatus that applies a load to a coreor ball and measures the number of inches the core or ball is deflectedat measured loads. A crude load/deflection curve is generated that isfit to the Atti compression scale that results in a number beinggenerated that represents an Atti compression. The DCM does this via aload cell attached to the bottom of a hydraulic cylinder that istriggered pneumatically at a fixed rate (typically about 1.0 ft/s)towards a stationary core. Attached to the cylinder is an LVDT thatmeasures the distance the cylinder travels during the testing timeframe.A software-based logarithmic algorithm ensures that measurements are nottaken until at least five successive increases in load are detectedduring the initial phase of the test. The SCDI is a slight variation ofthis set up. The hardware is the same, but the software and output haschanged. With the SCDI, the interest is in the pounds of force requiredto deflect a core x amount of inches. That amount of deflection is 10%percent of the core diameter. The DCM is triggered, the cylinderdeflects the core by 10% of its diameter, and the DCM reports back thepounds of force required (as measured from the attached load cell) todeflect the core by that amount. The value displayed is a single numberin units of pounds.

Drop Rebound.

By “drop rebound,” it is meant the number of inches a sphere willrebound when dropped from a height of 72 inches in this case, measuringfrom the bottom of the sphere. A scale, in inches is mounted directlybehind the path of the dropped sphere and the sphere is dropped onto aheavy, hard base such as a slab of marble or granite (typically about 1ft wide by 1 ft high by 1 ft deep). The test is carried out at about72-75° F. and about 50% RH

Coefficient of Restitution (“COR”).

The COR is determined according to a known procedure, wherein a golfball or golf ball subassembly (for example, a golf ball core) is firedfrom an air cannon at two given velocities and a velocity of 125 ft/s isused for the calculations. Ballistic light screens are located betweenthe air cannon and steel plate at a fixed distance to measure ballvelocity. As the ball travels toward the steel plate, it activates eachlight screen and the ball's time period at each light screen ismeasured. This provides an incoming transit time period which isinversely proportional to the ball's incoming velocity. The ball makesimpact with the steel plate and rebounds so it passes again through thelight screens. As the rebounding ball activates each light screen, theball's time period at each screen is measured. This provides an outgoingtransit time period which is inversely proportional to the ball'soutgoing velocity. The COR is then calculated as the ratio of the ball'soutgoing transit time period to the ball's incoming transit time period(COR=V_(out)/V_(in)=T_(in)/T_(out)).

Density.

The density refers to the weight per unit volume (typically, g/cm³) ofthe material and can be measured per ASTM D-1622.

It is understood that the golf ball compositions, constructions, andproducts described and illustrated herein represent only someembodiments of the invention. It is appreciated by those skilled in theart that various changes and additions can be made to compositions,constructions, and products without departing from the spirit and scopeof this invention. It is intended that all such embodiments be coveredby the appended claims.

We claim:
 1. A multi-layered golf ball, comprising: i) an inner corelayer comprising a non-foamed thermoset or thermoplastic composition,the inner core layer having a diameter in the range of about 0.750 toabout 1.500 inches; ii) an outer core layer comprising a foamedcomposition, the outer core layer being disposed about the inner corelayer and having a thickness in the range of about 0.025 to about 0.800inches, wherein the inner core has a specific gravity (SG_(inner)) andan outer surface hardness (H_(inner core surface)) and a center hardness(H_(inner core center)), the H_(inner core surface) being the same orless than the H_(inner core center) to provide a zero or negativehardness gradient; and the outer core has a specific gravity(SG_(outer)) and an outer surface hardness (H_(outer surface of OC)) anda midpoint hardness (H_(midpoint of OC)), the H_(outer surface of OC)being greater than the H_(midpoint of OC), to provide a positivehardness gradient; and the SG_(inner) is greater than the SG_(outer),the outer core layer further having a specific gravity gradient, whereinthe outer core layer has an outer surface specific gravity and amidpoint specific gravity, the outer surface specific gravity beinggreater than the midpoint specific gravity; and iii) a cover having atleast one layer disposed about the multi-layered core.
 2. The golf ballof claim 1, wherein the H_(inner core center) is in the range of about30 to about 95 Shore C and the H_(inner core surface) is in the range ofabout 30 to about 95 Shore C.
 3. The golf ball of claim 1, wherein the(H_(midpoint of OC)) is in the range of about 10 to about 55 Shore C andthe H_(outer surface of OC) is in the range of about 13 to about 60Shore C.
 4. The golf ball of claim 1, wherein the inner core has adiameter in the range of about 0.90 to about 1.40 inches and specificgravity in the range of about 0.60 to about 2.90 g/cc.
 5. The golf ballof claim 1, wherein the inner core layer comprises a thermoset rubberselected from the group consisting of polybutadiene, ethylene-propylenerubber, ethylene-propylene-diene rubber, polyisoprene, styrene-butadienerubber, polyalkenamers, and butyl rubber, and mixtures thereof.
 6. Thegolf ball of claim 5, wherein the thermoset rubber is polybutadienerubber.
 7. The golf ball of claim 1, wherein the inner core layercomprises a thermoplastic polymer selected from the group consisting ofpartially-neutralized ionomers; highly-neutralized ionomers; polyesters;polyamides; polyamide-ethers, polyamide-esters; polyurethanes,polyureas; fluoropolymers; polystyrenes; polypropylenes; polyethylenes;polyvinyl chlorides; polyvinyl acetates; polycarbonates; polyvinylalcohols; polyester-ethers; polyethers; polyimides, polyetherketones,polyamideimides; and mixtures thereof.
 8. The golf ball of claim 7,wherein the thermoplastic material is an ionomer composition comprisingan O/X/Y-type copolymer, wherein O is α-olefin, X is a C₃-C₈α,β-ethylenically unsaturated carboxylic acid present in an amount of 5to 20 wt. %, based on total weight of the copolymer, and Y is anacrylate selected from alkyl acrylates and aryl acrylates present in anamount of 0 to 50 wt. %, based on total weight of the copolymer, whereingreater than 70% of the acid groups present in the composition areneutralized with a metal ion.
 9. The golf ball of claim 1, wherein theouter core layer comprises a foamed polyurethane composition.
 10. Thegolf ball of claim 1, wherein the outer core layer has a thickness inthe range of about 0.050 to about 0.300 inches and specific gravity inthe range of about 0.20 to about 0.95 g/cc.
 11. A multi-layered golfball, comprising: i) an inner core layer comprising a non-foamedthermoset or thermoplastic composition, the inner core layer having adiameter in the range of about 0.750 to about 1.500 inches; ii) an outercore layer comprising a foamed composition, the outer core layer beingdisposed about the inner core layer and having a thickness in the rangeof about 0.025 to about 0.800 inches, wherein the inner core has aspecific gravity (SG_(inner)) and an outer surface hardness(H_(inner core surface)) and a center hardness (H_(inner core center)),the H_(inner core surface) being greater than the H_(inner core center)to provide a positive hardness gradient; and the outer core has aspecific gravity (SG_(outer)) and an outer surface hardness(H_(outer surface of OC)) and a midpoint hardness (H_(midpoint of OC)),the H_(outer surface of OC) being greater than the (H_(midpoint of OC)),to provide a positive hardness gradient; and the SG_(inner) is greaterthan the SG_(outer), the outer core layer further having a specificgravity gradient, wherein the outer core layer has an outer surfacespecific gravity and a midpoint specific gravity, the outer surfacespecific gravity being greater than the midpoint specific gravity; andiii) a cover having at least one layer disposed about the multi-layeredcore.
 12. The golf ball of claim 11, wherein the H_(inner core center)is in the range of about 30 to about 95 Shore C and theH_(inner core surface) is in the range of about 33 to about 98 Shore C.13. The golf ball of claim 11, wherein the H_(midpoint of OC) is in therange of about 10 to about 55 Shore C and the H_(outer surface of OC) isin the range of about 13 to about 60 Shore C.
 14. The golf ball of claim11, wherein the inner core layer comprises a thermoset rubber selectedfrom the group consisting of polybutadiene, ethylene-propylene rubber,ethylene-propylene-diene rubber, polyisoprene, styrene-butadiene rubber,polyalkenamers, and butyl rubber, and mixtures thereof.
 15. The golfball of claim 14, wherein the thermoset rubber is polybutadiene rubber.16. The golf ball of claim 11, wherein the inner core layer comprises athermoplastic polymer selected from the group consisting ofpartially-neutralized ionomers; highly-neutralized ionomers; polyesters;polyamides; polyamide-ethers, polyamide-esters; polyurethanes,polyureas; fluoropolymers; polystyrenes; polypropylenes; polyethylenes;polyvinyl chlorides; polyvinyl acetates; polycarbonates; polyvinylalcohols; polyester-ethers; polyethers; polyimides, polyetherketones,polyamideimides; and mixtures thereof.
 17. The golf ball of claim 16,wherein the thermoplastic material is an ionomer composition comprisingan O/X/Y-type copolymer, wherein O is α-olefin, X is a C₃-C₈α,β-ethylenically unsaturated carboxylic acid present in an amount of 5to 20 wt. %, based on total weight of the copolymer, and Y is anacrylate selected from alkyl acrylates and aryl acrylates present in anamount of 0 to 50 wt. %, based on total weight of the copolymer, whereingreater than 70% of the acid groups present in the composition areneutralized with a metal ion.
 18. The golf ball of claim 11, wherein theouter core layer comprises a foamed polyurethane composition.